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 $211.37   12.602%   $238.0068   $238.01   $238.00   $238.00  
  Purchase #2 $154.68   13.407%   $175.4179   $175.42   $175.40   $175.40  
  Purchase #3 $243.68   7.781%   $262.6407   $262.64   $262.65   $262.60  
  Purchase #4 $148.88   8.189%   $161.0718   $161.07   $161.05   $161.10  
  Purchase #5 $212.43   6.105%   $225.3989   $225.40   $225.40   $225.40  
  Purchase #6 $123.68   5.862%   $130.9301   $130.93   $130.95   $130.90  
  Purchase #7 $247.62   13.567%   $281.2146   $281.21   $281.20   $281.20  
  7 purchase totals = $1,342.34       $1,474.6808   $1,474.68   $1,474.65   $1,474.60