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 $104.30   11.237%   $116.0202   $116.02   $116.00   $116.00  
  Purchase #2 $54.98   4.167%   $57.271   $57.27   $57.25   $57.30  
  Purchase #3 $57.55   11.294%   $64.0497   $64.05   $64.05   $64.00  
  Purchase #4 $239.49   5.767%   $253.3014   $253.30   $253.30   $253.30  
  Purchase #5 $180.81   8.111%   $195.4755   $195.48   $195.50   $195.50  
  Purchase #6 $61.42   11.362%   $68.3985   $68.40   $68.40   $68.40  
  Purchase #7 $66.50   12.456%   $74.7832   $74.78   $74.80   $74.80  
  7 purchase totals = $765.05       $829.2995   $829.30   $829.30   $829.30