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 $59.97   13.656%   $68.1595   $68.16   $68.15   $68.20  
  Purchase #2 $99.63   11.189%   $110.7776   $110.78   $110.80   $110.80  
  Purchase #3 $104.33   3.290%   $107.7625   $107.76   $107.75   $107.80  
  Purchase #4 $125.95   7.781%   $135.7502   $135.75   $135.75   $135.80  
  Purchase #5 $217.28   8.825%   $236.455   $236.46   $236.45   $236.50  
  Purchase #6 $201.58   10.814%   $223.3789   $223.38   $223.40   $223.40  
  Purchase #7 $53.44   11.604%   $59.6412   $59.64   $59.65   $59.60  
  7 purchase totals = $862.18       $941.9249   $941.93   $941.95   $942.10