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 $180.49   8.507%   $195.8443   $195.84   $195.85   $195.80  
  Purchase #2 $209.41   11.531%   $233.5571   $233.56   $233.55   $233.60  
  Purchase #3 $130.38   9.214%   $142.3932   $142.39   $142.40   $142.40  
  Purchase #4 $7.63   8.417%   $8.2722   $8.27   $8.25   $8.30  
  Purchase #5 $88.49   6.449%   $94.1967   $94.20   $94.20   $94.20  
  Purchase #6 $50.32   10.123%   $55.4139   $55.41   $55.40   $55.40  
  Purchase #7 $6.47   8.781%   $7.0381   $7.04   $7.05   $7.00  
  7 purchase totals = $673.19       $736.7155   $736.71   $736.70   $736.70