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 $193.58   12.192%   $217.1813   $217.18   $217.20   $217.20  
  Purchase #2 $215.82   8.229%   $233.5798   $233.58   $233.60   $233.60  
  Purchase #3 $141.61   3.399%   $146.4233   $146.42   $146.40   $146.40  
  Purchase #4 $51.62   11.756%   $57.6884   $57.69   $57.70   $57.70  
  Purchase #5 $78.43   6.515%   $83.5397   $83.54   $83.55   $83.50  
  Purchase #6 $236.56   11.387%   $263.4971   $263.50   $263.50   $263.50  
  Purchase #7 $234.46   7.155%   $251.2356   $251.24   $251.25   $251.20  
  7 purchase totals = $1,152.08       $1,253.1452   $1,253.15   $1,253.20   $1,253.10