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 $68.34   11.260%   $76.0351   $76.04   $76.05   $76.00  
  Purchase #2 $170.62   12.593%   $192.1062   $192.11   $192.10   $192.10  
  Purchase #3 $62.39   8.271%   $67.5503   $67.55   $67.55   $67.60  
  Purchase #4 $60.64   7.872%   $65.4136   $65.41   $65.40   $65.40  
  Purchase #5 $100.43   5.193%   $105.6453   $105.65   $105.65   $105.60  
  Purchase #6 $241.27   11.134%   $268.133   $268.13   $268.15   $268.10  
  Purchase #7 $37.99   4.266%   $39.6107   $39.61   $39.60   $39.60  
  7 purchase totals = $741.68       $814.4942   $814.50   $814.50   $814.40