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 $210.80   11.216%   $234.4433   $234.44   $234.45   $234.40  
  Purchase #2 $114.29   10.222%   $125.9727   $125.97   $125.95   $126.00  
  Purchase #3 $154.84   8.779%   $168.4334   $168.43   $168.45   $168.40  
  Purchase #4 $237.94   6.354%   $253.0587   $253.06   $253.05   $253.10  
  Purchase #5 $49.53   7.569%   $53.2789   $53.28   $53.30   $53.30  
  Purchase #6 $172.78   12.730%   $194.7749   $194.77   $194.75   $194.80  
  Purchase #7 $210.41   7.316%   $225.8036   $225.80   $225.80   $225.80  
  7 purchase totals = $1,150.59       $1,255.7655   $1,255.75   $1,255.75   $1,255.80