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 $63.46   6.621%   $67.6617   $67.66   $67.65   $67.70  
  Purchase #2 $156.88   4.324%   $163.6635   $163.66   $163.65   $163.70  
  Purchase #3 $230.47   13.464%   $261.5005   $261.50   $261.50   $261.50  
  Purchase #4 $195.45   4.186%   $203.6315   $203.63   $203.65   $203.60  
  Purchase #5 $172.96   6.225%   $183.7268   $183.73   $183.75   $183.70  
  Purchase #6 $83.61   4.265%   $87.176   $87.18   $87.20   $87.20  
  Purchase #7 $131.92   8.599%   $143.2638   $143.26   $143.25   $143.30  
  7 purchase totals = $1,034.75       $1,110.6238   $1,110.62   $1,110.65   $1,110.70