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 $203.38   3.236%   $209.9614   $209.96   $209.95   $210.00  
  Purchase #2 $64.84   4.272%   $67.61   $67.61   $67.60   $67.60  
  Purchase #3 $13.67   10.822%   $15.1494   $15.15   $15.15   $15.10  
  Purchase #4 $175.78   13.665%   $199.8003   $199.80   $199.80   $199.80  
  Purchase #5 $243.27   7.635%   $261.8437   $261.84   $261.85   $261.80  
  Purchase #6 $52.87   10.494%   $58.4182   $58.42   $58.40   $58.40  
  Purchase #7 $239.83   11.564%   $267.5639   $267.56   $267.55   $267.60  
  7 purchase totals = $993.64       $1,080.3469   $1,080.34   $1,080.30   $1,080.30