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 $60.48   12.808%   $68.2263   $68.23   $68.25   $68.20  
  Purchase #2 $180.54   13.322%   $204.5915   $204.59   $204.60   $204.60  
  Purchase #3 $119.87   4.827%   $125.6561   $125.66   $125.65   $125.70  
  Purchase #4 $233.84   13.862%   $266.2549   $266.25   $266.25   $266.30  
  Purchase #5 $78.33   9.856%   $86.0502   $86.05   $86.05   $86.10  
  Purchase #6 $109.43   11.822%   $122.3668   $122.37   $122.35   $122.40  
  Purchase #7 $236.61   12.614%   $266.456   $266.46   $266.45   $266.50  
  7 purchase totals = $1,019.10       $1,139.6018   $1,139.61   $1,139.60   $1,139.80