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 $62.73   10.323%   $69.2056   $69.21   $69.20   $69.20  
  Purchase #2 $206.46   5.102%   $216.9936   $216.99   $217.00   $217.00  
  Purchase #3 $236.82   3.552%   $245.2318   $245.23   $245.25   $245.20  
  Purchase #4 $31.44   12.140%   $35.2568   $35.26   $35.25   $35.30  
  Purchase #5 $22.93   5.189%   $24.1198   $24.12   $24.10   $24.10  
  Purchase #6 $229.90   3.268%   $237.4131   $237.41   $237.40   $237.40  
  Purchase #7 $229.88   12.322%   $258.2058   $258.21   $258.20   $258.20  
  7 purchase totals = $1,020.16       $1,086.4265   $1,086.43   $1,086.40   $1,086.40