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 $211.71   9.795%   $232.447   $232.45   $232.45   $232.40  
  Purchase #2 $219.49   8.840%   $238.8929   $238.89   $238.90   $238.90  
  Purchase #3 $32.75   9.603%   $35.895   $35.90   $35.90   $35.90  
  Purchase #4 $50.44   10.158%   $55.5637   $55.56   $55.55   $55.60  
  Purchase #5 $221.78   3.240%   $228.9657   $228.97   $228.95   $229.00  
  Purchase #6 $162.86   5.122%   $171.2017   $171.20   $171.20   $171.20  
  Purchase #7 $18.84   9.471%   $20.6243   $20.62   $20.60   $20.60  
  7 purchase totals = $917.87       $983.5903   $983.59   $983.55   $983.60