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 $241.74   11.176%   $268.7569   $268.76   $268.75   $268.80  
  Purchase #2 $9.34   10.372%   $10.3087   $10.31   $10.30   $10.30  
  Purchase #3 $86.53   3.154%   $89.2592   $89.26   $89.25   $89.30  
  Purchase #4 $109.60   8.180%   $118.5653   $118.57   $118.55   $118.60  
  Purchase #5 $187.95   4.143%   $195.7368   $195.74   $195.75   $195.70  
  Purchase #6 $237.38   9.568%   $260.0925   $260.09   $260.10   $260.10  
  Purchase #7 $84.84   7.168%   $90.9213   $90.92   $90.90   $90.90  
  7 purchase totals = $957.38       $1,033.6407   $1,033.65   $1,033.60   $1,033.70