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 $222.62   6.747%   $237.6402   $237.64   $237.65   $237.60  
  Purchase #2 $176.46   3.369%   $182.4049   $182.40   $182.40   $182.40  
  Purchase #3 $140.36   3.209%   $144.8642   $144.86   $144.85   $144.90  
  Purchase #4 $203.76   4.223%   $212.3648   $212.36   $212.35   $212.40  
  Purchase #5 $161.77   11.669%   $180.6469   $180.65   $180.65   $180.60  
  Purchase #6 $217.38   7.819%   $234.3769   $234.38   $234.40   $234.40  
  Purchase #7 $140.78   13.581%   $159.8993   $159.90   $159.90   $159.90  
  7 purchase totals = $1,263.13       $1,352.1972   $1,352.19   $1,352.20   $1,352.20