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 $241.63   10.606%   $267.2573   $267.26   $267.25   $267.30  
  Purchase #2 $50.58   13.742%   $57.5307   $57.53   $57.55   $57.50  
  Purchase #3 $101.70   8.423%   $110.2662   $110.27   $110.25   $110.30  
  Purchase #4 $46.33   13.466%   $52.5688   $52.57   $52.55   $52.60  
  Purchase #5 $122.51   3.414%   $126.6925   $126.69   $126.70   $126.70  
  Purchase #6 $137.50   10.622%   $152.1053   $152.11   $152.10   $152.10  
  Purchase #7 $194.45   6.607%   $207.2973   $207.30   $207.30   $207.30  
  7 purchase totals = $894.70       $973.7181   $973.73   $973.70   $973.80