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 $224.38   12.207%   $251.7701   $251.77   $251.75   $251.80  
  Purchase #2 $161.34   13.142%   $182.5433   $182.54   $182.55   $182.50  
  Purchase #3 $103.29   13.754%   $117.4965   $117.50   $117.50   $117.50  
  Purchase #4 $85.97   13.170%   $97.2922   $97.29   $97.30   $97.30  
  Purchase #5 $207.58   9.546%   $227.3956   $227.40   $227.40   $227.40  
  Purchase #6 $190.98   13.514%   $216.789   $216.79   $216.80   $216.80  
  Purchase #7 $241.47   5.712%   $255.2628   $255.26   $255.25   $255.30  
  7 purchase totals = $1,215.01       $1,348.5495   $1,348.55   $1,348.55   $1,348.60