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 $42.81   12.361%   $48.1017   $48.10   $48.10   $48.10  
  Purchase #2 $234.95   11.227%   $261.3278   $261.33   $261.35   $261.30  
  Purchase #3 $83.58   4.167%   $87.0628   $87.06   $87.05   $87.10  
  Purchase #4 $209.91   3.796%   $217.8782   $217.88   $217.90   $217.90  
  Purchase #5 $108.70   3.559%   $112.5686   $112.57   $112.55   $112.60  
  Purchase #6 $243.33   13.176%   $275.3912   $275.39   $275.40   $275.40  
  Purchase #7 $118.64   4.862%   $124.4083   $124.41   $124.40   $124.40  
  7 purchase totals = $1,041.92       $1,126.7386   $1,126.74   $1,126.75   $1,126.80