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 $186.57   4.238%   $194.4768   $194.48   $194.50   $194.50  
  Purchase #2 $223.58   11.796%   $249.9535   $249.95   $249.95   $250.00  
  Purchase #3 $234.62   8.105%   $253.636   $253.64   $253.65   $253.60  
  Purchase #4 $125.50   11.772%   $140.2739   $140.27   $140.25   $140.30  
  Purchase #5 $230.62   10.864%   $255.6746   $255.67   $255.65   $255.70  
  Purchase #6 $250.73   4.171%   $261.1879   $261.19   $261.20   $261.20  
  Purchase #7 $216.65   7.538%   $232.9811   $232.98   $233.00   $233.00  
  7 purchase totals = $1,468.27       $1,588.1838   $1,588.18   $1,588.20   $1,588.30