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 $211.95   12.399%   $238.2297   $238.23   $238.25   $238.20  
  Purchase #2 $41.88   9.276%   $45.7648   $45.76   $45.75   $45.80  
  Purchase #3 $65.31   6.194%   $69.3553   $69.36   $69.35   $69.40  
  Purchase #4 $101.63   12.313%   $114.1437   $114.14   $114.15   $114.10  
  Purchase #5 $110.77   13.184%   $125.3739   $125.37   $125.35   $125.40  
  Purchase #6 $146.63   6.758%   $156.5393   $156.54   $156.55   $156.50  
  Purchase #7 $250.92   8.301%   $271.7489   $271.75   $271.75   $271.70  
  7 purchase totals = $929.09       $1,021.1556   $1,021.15   $1,021.15   $1,021.10