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 $225.74   7.197%   $241.9865   $241.99   $242.00   $242.00  
  Purchase #2 $200.87   6.859%   $214.6477   $214.65   $214.65   $214.60  
  Purchase #3 $53.88   11.742%   $60.2066   $60.21   $60.20   $60.20  
  Purchase #4 $48.63   5.695%   $51.3995   $51.40   $51.40   $51.40  
  Purchase #5 $45.76   7.269%   $49.0863   $49.09   $49.10   $49.10  
  Purchase #6 $72.67   4.571%   $75.9917   $75.99   $76.00   $76.00  
  Purchase #7 $119.58   9.264%   $130.6579   $130.66   $130.65   $130.70  
  7 purchase totals = $767.13       $823.9762   $823.99   $824.00   $824.00