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 $239.60   4.233%   $249.7423   $249.74   $249.75   $249.70  
  Purchase #2 $62.39   9.490%   $68.3108   $68.31   $68.30   $68.30  
  Purchase #3 $223.25   9.644%   $244.7802   $244.78   $244.80   $244.80  
  Purchase #4 $113.40   5.390%   $119.5123   $119.51   $119.50   $119.50  
  Purchase #5 $152.54   10.159%   $168.0365   $168.04   $168.05   $168.00  
  Purchase #6 $131.45   12.627%   $148.0482   $148.05   $148.05   $148.00  
  Purchase #7 $243.39   7.512%   $261.6735   $261.67   $261.65   $261.70  
  7 purchase totals = $1,166.02       $1,260.1038   $1,260.10   $1,260.10   $1,260.00