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 $41.77   13.110%   $47.246   $47.25   $47.25   $47.20  
  Purchase #2 $167.42   9.868%   $183.941   $183.94   $183.95   $183.90  
  Purchase #3 $48.62   11.256%   $54.0927   $54.09   $54.10   $54.10  
  Purchase #4 $234.50   11.709%   $261.9576   $261.96   $261.95   $262.00  
  Purchase #5 $98.29   9.663%   $107.7878   $107.79   $107.80   $107.80  
  Purchase #6 $104.83   3.385%   $108.3785   $108.38   $108.40   $108.40  
  Purchase #7 $160.32   8.491%   $173.9328   $173.93   $173.95   $173.90  
  7 purchase totals = $855.75       $937.3364   $937.34   $937.40   $937.30