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 $58.61   13.635%   $66.6015   $66.60   $66.60   $66.60  
  Purchase #2 $159.40   3.491%   $164.9647   $164.96   $164.95   $165.00  
  Purchase #3 $84.42   11.331%   $93.9856   $93.99   $94.00   $94.00  
  Purchase #4 $200.91   4.203%   $209.3542   $209.35   $209.35   $209.40  
  Purchase #5 $248.76   10.730%   $275.4519   $275.45   $275.45   $275.50  
  Purchase #6 $131.50   5.670%   $138.9561   $138.96   $138.95   $139.00  
  Purchase #7 $42.41   13.126%   $47.9767   $47.98   $48.00   $48.00  
  7 purchase totals = $926.01       $997.2907   $997.29   $997.30   $997.50