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 $111.69   11.244%   $124.2484   $124.25   $124.25   $124.20  
  Purchase #2 $77.50   10.473%   $85.6166   $85.62   $85.60   $85.60  
  Purchase #3 $206.63   12.233%   $231.907   $231.91   $231.90   $231.90  
  Purchase #4 $53.61   3.837%   $55.667   $55.67   $55.65   $55.70  
  Purchase #5 $248.42   3.250%   $256.4937   $256.49   $256.50   $256.50  
  Purchase #6 $30.82   9.216%   $33.6604   $33.66   $33.65   $33.70  
  Purchase #7 $117.44   6.516%   $125.0924   $125.09   $125.10   $125.10  
  7 purchase totals = $846.11       $912.6855   $912.69   $912.65   $912.70