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 $96.78   5.309%   $101.9181   $101.92   $101.90   $101.90  
  Purchase #2 $34.41   3.508%   $35.6171   $35.62   $35.60   $35.60  
  Purchase #3 $227.77   7.448%   $244.7343   $244.73   $244.75   $244.70  
  Purchase #4 $170.86   5.451%   $180.1736   $180.17   $180.15   $180.20  
  Purchase #5 $192.90   7.553%   $207.4697   $207.47   $207.45   $207.50  
  Purchase #6 $58.59   5.132%   $61.5968   $61.60   $61.60   $61.60  
  Purchase #7 $143.86   4.291%   $150.033   $150.03   $150.05   $150.00  
  7 purchase totals = $925.17       $981.5426   $981.54   $981.50   $981.50