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 $232.61   10.123%   $256.1571   $256.16   $256.15   $256.20  
  Purchase #2 $112.47   8.657%   $122.2065   $122.21   $122.20   $122.20  
  Purchase #3 $196.82   11.342%   $219.1433   $219.14   $219.15   $219.10  
  Purchase #4 $123.46   7.713%   $132.9825   $132.98   $133.00   $133.00  
  Purchase #5 $49.46   8.686%   $53.7561   $53.76   $53.75   $53.80  
  Purchase #6 $108.26   10.502%   $119.6295   $119.63   $119.65   $119.60  
  Purchase #7 $246.77   13.516%   $280.1234   $280.12   $280.10   $280.10  
  7 purchase totals = $1,069.85       $1,183.9984   $1,184.00   $1,184.00   $1,184.00