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 $69.34   5.633%   $73.2459   $73.25   $73.25   $73.20  
  Purchase #2 $98.57   13.589%   $111.9647   $111.96   $111.95   $112.00  
  Purchase #3 $172.92   6.288%   $183.7932   $183.79   $183.80   $183.80  
  Purchase #4 $53.76   11.187%   $59.7741   $59.77   $59.75   $59.80  
  Purchase #5 $244.91   3.449%   $253.3569   $253.36   $253.35   $253.40  
  Purchase #6 $13.49   8.823%   $14.6802   $14.68   $14.70   $14.70  
  Purchase #7 $215.95   6.787%   $230.6065   $230.61   $230.60   $230.60  
  7 purchase totals = $868.94       $927.4215   $927.42   $927.40   $927.50