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 $101.92   12.249%   $114.4042   $114.40   $114.40   $114.40  
  Purchase #2 $180.29   4.219%   $187.8964   $187.90   $187.90   $187.90  
  Purchase #3 $25.99   6.106%   $27.5769   $27.58   $27.60   $27.60  
  Purchase #4 $58.34   10.370%   $64.3899   $64.39   $64.40   $64.40  
  Purchase #5 $213.76   12.742%   $240.9973   $241.00   $241.00   $241.00  
  Purchase #6 $104.78   13.665%   $119.0982   $119.10   $119.10   $119.10  
  Purchase #7 $173.61   7.465%   $186.57   $186.57   $186.55   $186.60  
  7 purchase totals = $858.69       $940.9329   $940.94   $940.95   $941.00