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 $212.58   10.645%   $235.2091   $235.21   $235.20   $235.20  
  Purchase #2 $112.97   11.489%   $125.9491   $125.95   $125.95   $125.90  
  Purchase #3 $46.83   4.117%   $48.758   $48.76   $48.75   $48.80  
  Purchase #4 $195.93   5.267%   $206.2496   $206.25   $206.25   $206.20  
  Purchase #5 $75.48   4.184%   $78.6381   $78.64   $78.65   $78.60  
  Purchase #6 $203.81   5.139%   $214.2838   $214.28   $214.30   $214.30  
  Purchase #7 $101.42   8.208%   $109.7446   $109.74   $109.75   $109.70  
  7 purchase totals = $949.02       $1,018.8323   $1,018.83   $1,018.85   $1,018.70