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 $86.58   9.629%   $94.9168   $94.92   $94.90   $94.90  
  Purchase #2 $175.73   13.440%   $199.3481   $199.35   $199.35   $199.30  
  Purchase #3 $39.92   13.201%   $45.1898   $45.19   $45.20   $45.20  
  Purchase #4 $71.80   6.420%   $76.4096   $76.41   $76.40   $76.40  
  Purchase #5 $10.44   3.222%   $10.7764   $10.78   $10.80   $10.80  
  Purchase #6 $78.90   12.182%   $88.5116   $88.51   $88.50   $88.50  
  Purchase #7 $84.63   7.497%   $90.9747   $90.97   $90.95   $91.00  
  7 purchase totals = $548.00       $606.1270   $606.13   $606.10   $606.10