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 $199.80   13.282%   $226.3374   $226.34   $226.35   $226.30  
  Purchase #2 $6.62   3.863%   $6.8757   $6.88   $6.90   $6.90  
  Purchase #3 $34.46   5.690%   $36.4208   $36.42   $36.40   $36.40  
  Purchase #4 $217.66   10.198%   $239.857   $239.86   $239.85   $239.90  
  Purchase #5 $117.77   6.521%   $125.4498   $125.45   $125.45   $125.40  
  Purchase #6 $94.49   4.237%   $98.4935   $98.49   $98.50   $98.50  
  Purchase #7 $55.59   11.754%   $62.124   $62.12   $62.10   $62.10  
  7 purchase totals = $726.39       $795.5582   $795.56   $795.55   $795.50