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 $88.85   8.306%   $96.2299   $96.23   $96.25   $96.20  
  Purchase #2 $164.48   5.534%   $173.5823   $173.58   $173.60   $173.60  
  Purchase #3 $199.94   7.666%   $215.2674   $215.27   $215.25   $215.30  
  Purchase #4 $60.84   8.483%   $66.0011   $66.00   $66.00   $66.00  
  Purchase #5 $143.95   11.503%   $160.5086   $160.51   $160.50   $160.50  
  Purchase #6 $144.60   10.466%   $159.7338   $159.73   $159.75   $159.70  
  Purchase #7 $119.62   5.476%   $126.1704   $126.17   $126.15   $126.20  
  7 purchase totals = $922.28       $997.4935   $997.49   $997.50   $997.50