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 $82.53   12.130%   $92.5409   $92.54   $92.55   $92.50  
  Purchase #2 $183.57   10.697%   $203.2065   $203.21   $203.20   $203.20  
  Purchase #3 $112.81   5.615%   $119.1443   $119.14   $119.15   $119.10  
  Purchase #4 $10.80   8.578%   $11.7264   $11.73   $11.75   $11.70  
  Purchase #5 $37.64   5.224%   $39.6063   $39.61   $39.60   $39.60  
  Purchase #6 $174.42   12.616%   $196.4248   $196.42   $196.40   $196.40  
  Purchase #7 $242.34   12.104%   $271.6728   $271.67   $271.65   $271.70  
  7 purchase totals = $844.11       $934.3220   $934.32   $934.30   $934.20