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 $92.63   13.220%   $104.8757   $104.88   $104.90   $104.90  
  Purchase #2 $98.39   12.295%   $110.4871   $110.49   $110.50   $110.50  
  Purchase #3 $10.58   5.862%   $11.2002   $11.20   $11.20   $11.20  
  Purchase #4 $114.34   8.343%   $123.8794   $123.88   $123.90   $123.90  
  Purchase #5 $199.42   6.662%   $212.7054   $212.71   $212.70   $212.70  
  Purchase #6 $236.75   4.594%   $247.6263   $247.63   $247.65   $247.60  
  Purchase #7 $127.27   4.846%   $133.4375   $133.44   $133.45   $133.40  
  7 purchase totals = $879.38       $944.2116   $944.23   $944.30   $944.20