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 $60.44   12.567%   $68.0355   $68.04   $68.05   $68.00  
  Purchase #2 $93.78   11.634%   $104.6904   $104.69   $104.70   $104.70  
  Purchase #3 $139.77   7.600%   $150.3925   $150.39   $150.40   $150.40  
  Purchase #4 $111.96   12.820%   $126.3133   $126.31   $126.30   $126.30  
  Purchase #5 $98.77   9.590%   $108.242   $108.24   $108.25   $108.20  
  Purchase #6 $58.31   13.794%   $66.3533   $66.35   $66.35   $66.40  
  Purchase #7 $190.89   8.642%   $207.3867   $207.39   $207.40   $207.40  
  7 purchase totals = $753.92       $831.4137   $831.41   $831.45   $831.40