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 $237.69   12.466%   $267.3204   $267.32   $267.30   $267.30  
  Purchase #2 $136.29   6.873%   $145.6572   $145.66   $145.65   $145.70  
  Purchase #3 $192.38   11.107%   $213.7476   $213.75   $213.75   $213.70  
  Purchase #4 $238.92   13.639%   $271.5063   $271.51   $271.50   $271.50  
  Purchase #5 $248.42   5.117%   $261.1317   $261.13   $261.15   $261.10  
  Purchase #6 $106.91   11.673%   $119.3896   $119.39   $119.40   $119.40  
  Purchase #7 $89.57   9.508%   $98.0863   $98.09   $98.10   $98.10  
  7 purchase totals = $1,250.18       $1,376.8391   $1,376.85   $1,376.85   $1,376.80