Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.59   10.831%   $230.0741   $230.07   $230.05   $230.10  
  Purchase #2 $232.99   12.175%   $261.3565   $261.36   $261.35   $261.40  
  Purchase #3 $157.94   7.602%   $169.9466   $169.95   $169.95   $169.90  
  Purchase #4 $219.59   5.422%   $231.4962   $231.50   $231.50   $231.50  
  Purchase #5 $102.26   3.258%   $105.5916   $105.59   $105.60   $105.60  
  Purchase #6 $236.47   4.107%   $246.1818   $246.18   $246.20   $246.20  
  Purchase #7 $146.67   12.432%   $164.904   $164.90   $164.90   $164.90  
  7 purchase totals = $1,303.51       $1,409.5508   $1,409.55   $1,409.55   $1,409.60