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 $53.27   8.413%   $57.7516   $57.75   $57.75   $57.80  
  Purchase #2 $92.31   10.217%   $101.7413   $101.74   $101.75   $101.70  
  Purchase #3 $114.76   9.499%   $125.6611   $125.66   $125.65   $125.70  
  Purchase #4 $71.46   10.178%   $78.7332   $78.73   $78.75   $78.70  
  Purchase #5 $168.25   7.801%   $181.3752   $181.38   $181.40   $181.40  
  Purchase #6 $104.69   3.485%   $108.3384   $108.34   $108.35   $108.30  
  Purchase #7 $193.56   9.403%   $211.7604   $211.76   $211.75   $211.80  
  7 purchase totals = $798.30       $865.3612   $865.36   $865.40   $865.40