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 $199.89   3.307%   $206.5004   $206.50   $206.50   $206.50  
  Purchase #2 $22.50   3.319%   $23.2468   $23.25   $23.25   $23.20  
  Purchase #3 $177.76   4.274%   $185.3575   $185.36   $185.35   $185.40  
  Purchase #4 $231.47   5.628%   $244.4971   $244.50   $244.50   $244.50  
  Purchase #5 $131.39   4.710%   $137.5785   $137.58   $137.60   $137.60  
  Purchase #6 $124.74   4.483%   $130.3321   $130.33   $130.35   $130.30  
  Purchase #7 $111.61   9.532%   $122.2487   $122.25   $122.25   $122.20  
  7 purchase totals = $999.36       $1,049.7611   $1,049.77   $1,049.80   $1,049.70