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 $183.61   11.288%   $204.3359   $204.34   $204.35   $204.30  
  Purchase #2 $203.67   6.671%   $217.2568   $217.26   $217.25   $217.30  
  Purchase #3 $85.94   8.688%   $93.4065   $93.41   $93.40   $93.40  
  Purchase #4 $171.68   7.544%   $184.6315   $184.63   $184.65   $184.60  
  Purchase #5 $105.49   13.633%   $119.8715   $119.87   $119.85   $119.90  
  Purchase #6 $92.92   9.266%   $101.53   $101.53   $101.55   $101.50  
  Purchase #7 $215.91   13.641%   $245.3623   $245.36   $245.35   $245.40  
  7 purchase totals = $1,059.22       $1,166.3945   $1,166.40   $1,166.40   $1,166.40