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 $210.79   12.365%   $236.8542   $236.85   $236.85   $236.90  
  Purchase #2 $189.26   3.116%   $195.1573   $195.16   $195.15   $195.20  
  Purchase #3 $244.89   11.382%   $272.7634   $272.76   $272.75   $272.80  
  Purchase #4 $173.91   13.650%   $197.6487   $197.65   $197.65   $197.60  
  Purchase #5 $189.26   9.872%   $207.9437   $207.94   $207.95   $207.90  
  Purchase #6 $105.79   3.314%   $109.2959   $109.30   $109.30   $109.30  
  Purchase #7 $230.64   11.519%   $257.2074   $257.21   $257.20   $257.20  
  7 purchase totals = $1,344.54       $1,476.8706   $1,476.87   $1,476.85   $1,476.90