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 $76.66   13.503%   $87.0114   $87.01   $87.00   $87.00  
  Purchase #2 $105.69   6.607%   $112.6729   $112.67   $112.65   $112.70  
  Purchase #3 $126.30   4.554%   $132.0517   $132.05   $132.05   $132.10  
  Purchase #4 $241.88   8.322%   $262.0093   $262.01   $262.00   $262.00  
  Purchase #5 $56.90   6.710%   $60.718   $60.72   $60.70   $60.70  
  Purchase #6 $56.88   6.344%   $60.4885   $60.49   $60.50   $60.50  
  Purchase #7 $87.99   3.650%   $91.2016   $91.20   $91.20   $91.20  
  7 purchase totals = $752.30       $806.1534   $806.15   $806.10   $806.20