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 $111.81   13.251%   $126.6259   $126.63   $126.65   $126.60  
  Purchase #2 $143.31   5.734%   $151.5274   $151.53   $151.55   $151.50  
  Purchase #3 $169.69   8.197%   $183.5995   $183.60   $183.60   $183.60  
  Purchase #4 $101.49   13.551%   $115.2429   $115.24   $115.25   $115.20  
  Purchase #5 $162.37   13.145%   $183.7135   $183.71   $183.70   $183.70  
  Purchase #6 $139.54   13.553%   $158.4519   $158.45   $158.45   $158.50  
  Purchase #7 $102.70   12.519%   $115.557   $115.56   $115.55   $115.60  
  7 purchase totals = $930.91       $1,034.7181   $1,034.72   $1,034.75   $1,034.70