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 $66.36   8.746%   $72.1638   $72.16   $72.15   $72.20  
  Purchase #2 $79.63   7.144%   $85.3188   $85.32   $85.30   $85.30  
  Purchase #3 $123.30   7.432%   $132.4637   $132.46   $132.45   $132.50  
  Purchase #4 $26.69   9.338%   $29.1823   $29.18   $29.20   $29.20  
  Purchase #5 $104.67   11.541%   $116.75   $116.75   $116.75   $116.80  
  Purchase #6 $42.44   8.704%   $46.134   $46.13   $46.15   $46.10  
  Purchase #7 $225.38   11.785%   $251.941   $251.94   $251.95   $251.90  
  7 purchase totals = $668.47       $733.9536   $733.94   $733.95   $734.00