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 $208.36   13.403%   $236.2865   $236.29   $236.30   $236.30  
  Purchase #2 $53.91   9.195%   $58.867   $58.87   $58.85   $58.90  
  Purchase #3 $169.27   13.626%   $192.3347   $192.33   $192.35   $192.30  
  Purchase #4 $22.41   4.585%   $23.4375   $23.44   $23.45   $23.40  
  Purchase #5 $188.31   9.848%   $206.8548   $206.85   $206.85   $206.90  
  Purchase #6 $118.60   12.506%   $133.4321   $133.43   $133.45   $133.40  
  Purchase #7 $29.44   11.328%   $32.775   $32.78   $32.80   $32.80  
  7 purchase totals = $790.30       $883.9876   $883.99   $884.05   $884.00