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 $214.63   5.749%   $226.9691   $226.97   $226.95   $227.00  
  Purchase #2 $151.98   6.372%   $161.6642   $161.66   $161.65   $161.70  
  Purchase #3 $102.55   9.484%   $112.2758   $112.28   $112.30   $112.30  
  Purchase #4 $97.79   11.676%   $109.208   $109.21   $109.20   $109.20  
  Purchase #5 $242.25   13.172%   $274.1592   $274.16   $274.15   $274.20  
  Purchase #6 $205.38   3.421%   $212.406   $212.41   $212.40   $212.40  
  Purchase #7 $226.29   7.512%   $243.2889   $243.29   $243.30   $243.30  
  7 purchase totals = $1,240.87       $1,339.9712   $1,339.98   $1,339.95   $1,340.10