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 $202.87   11.388%   $225.9728   $225.97   $225.95   $226.00  
  Purchase #2 $59.41   10.872%   $65.8691   $65.87   $65.85   $65.90  
  Purchase #3 $221.61   12.800%   $249.9761   $249.98   $250.00   $250.00  
  Purchase #4 $98.98   6.738%   $105.6493   $105.65   $105.65   $105.60  
  Purchase #5 $205.64   13.658%   $233.7263   $233.73   $233.75   $233.70  
  Purchase #6 $209.72   9.308%   $229.2407   $229.24   $229.25   $229.20  
  Purchase #7 $213.68   5.189%   $224.7679   $224.77   $224.75   $224.80  
  7 purchase totals = $1,211.91       $1,335.2022   $1,335.21   $1,335.20   $1,335.20