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 $64.39   5.646%   $68.0255   $68.03   $68.05   $68.00  
  Purchase #2 $162.92   8.211%   $176.2974   $176.30   $176.30   $176.30  
  Purchase #3 $56.55   13.733%   $64.316   $64.32   $64.30   $64.30  
  Purchase #4 $200.87   4.585%   $210.0799   $210.08   $210.10   $210.10  
  Purchase #5 $89.61   5.748%   $94.7608   $94.76   $94.75   $94.80  
  Purchase #6 $234.88   13.541%   $266.6851   $266.69   $266.70   $266.70  
  Purchase #7 $92.70   9.800%   $101.7846   $101.78   $101.80   $101.80  
  7 purchase totals = $901.92       $981.9493   $981.96   $982.00   $982.00