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 $72.44   7.716%   $78.0295   $78.03   $78.05   $78.00  
  Purchase #2 $185.89   5.242%   $195.6344   $195.63   $195.65   $195.60  
  Purchase #3 $161.67   7.472%   $173.75   $173.75   $173.75   $173.80  
  Purchase #4 $215.38   11.174%   $239.4466   $239.45   $239.45   $239.40  
  Purchase #5 $96.55   7.742%   $104.0249   $104.02   $104.00   $104.00  
  Purchase #6 $183.53   8.446%   $199.0309   $199.03   $199.05   $199.00  
  Purchase #7 $49.83   3.115%   $51.3822   $51.38   $51.40   $51.40  
  7 purchase totals = $965.29       $1,041.2985   $1,041.29   $1,041.35   $1,041.20