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 $207.73   6.527%   $221.2885   $221.29   $221.30   $221.30  
  Purchase #2 $29.59   8.419%   $32.0812   $32.08   $32.10   $32.10  
  Purchase #3 $161.55   9.248%   $176.4901   $176.49   $176.50   $176.50  
  Purchase #4 $194.90   8.149%   $210.7824   $210.78   $210.80   $210.80  
  Purchase #5 $30.55   6.303%   $32.4756   $32.48   $32.50   $32.50  
  Purchase #6 $107.76   4.688%   $112.8118   $112.81   $112.80   $112.80  
  Purchase #7 $168.51   8.164%   $182.2672   $182.27   $182.25   $182.30  
  7 purchase totals = $900.59       $968.1968   $968.20   $968.25   $968.30