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 $231.87   5.872%   $245.4854   $245.49   $245.50   $245.50  
  Purchase #2 $178.54   13.605%   $202.8304   $202.83   $202.85   $202.80  
  Purchase #3 $51.80   11.251%   $57.628   $57.63   $57.65   $57.60  
  Purchase #4 $133.91   7.862%   $144.438   $144.44   $144.45   $144.40  
  Purchase #5 $58.67   6.540%   $62.507   $62.51   $62.50   $62.50  
  Purchase #6 $164.96   7.752%   $177.7477   $177.75   $177.75   $177.70  
  Purchase #7 $20.35   6.339%   $21.64   $21.64   $21.65   $21.60  
  7 purchase totals = $840.10       $912.2765   $912.29   $912.35   $912.10