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 $67.97   11.268%   $75.6289   $75.63   $75.65   $75.60  
  Purchase #2 $78.32   10.322%   $86.4042   $86.40   $86.40   $86.40  
  Purchase #3 $245.56   4.574%   $256.7919   $256.79   $256.80   $256.80  
  Purchase #4 $79.58   6.179%   $84.4972   $84.50   $84.50   $84.50  
  Purchase #5 $85.60   7.736%   $92.222   $92.22   $92.20   $92.20  
  Purchase #6 $157.61   6.872%   $168.441   $168.44   $168.45   $168.40  
  Purchase #7 $29.49   8.552%   $32.012   $32.01   $32.00   $32.00  
  7 purchase totals = $744.13       $795.9972   $795.99   $796.00   $795.90