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 $41.32   8.484%   $44.8256   $44.83   $44.85   $44.80  
  Purchase #2 $197.62   13.428%   $224.1564   $224.16   $224.15   $224.20  
  Purchase #3 $119.71   13.318%   $135.653   $135.65   $135.65   $135.70  
  Purchase #4 $25.89   6.588%   $27.5956   $27.60   $27.60   $27.60  
  Purchase #5 $237.56   5.293%   $250.1341   $250.13   $250.15   $250.10  
  Purchase #6 $225.78   11.343%   $251.3902   $251.39   $251.40   $251.40  
  Purchase #7 $161.53   9.610%   $177.053   $177.05   $177.05   $177.10  
  7 purchase totals = $1,009.41       $1,110.8079   $1,110.81   $1,110.85   $1,110.90