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 $188.84   8.298%   $204.5099   $204.51   $204.50   $204.50  
  Purchase #2 $100.88   11.176%   $112.1543   $112.15   $112.15   $112.20  
  Purchase #3 $61.46   13.283%   $69.6237   $69.62   $69.60   $69.60  
  Purchase #4 $8.53   4.719%   $8.9325   $8.93   $8.95   $8.90  
  Purchase #5 $136.81   11.211%   $152.1478   $152.15   $152.15   $152.10  
  Purchase #6 $144.43   6.158%   $153.324   $153.32   $153.30   $153.30  
  Purchase #7 $22.67   12.255%   $25.4482   $25.45   $25.45   $25.40  
  7 purchase totals = $663.62       $726.1404   $726.13   $726.10   $726.00