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 $118.74   4.521%   $124.1082   $124.11   $124.10   $124.10  
  Purchase #2 $78.61   6.602%   $83.7998   $83.80   $83.80   $83.80  
  Purchase #3 $183.26   8.147%   $198.1902   $198.19   $198.20   $198.20  
  Purchase #4 $42.45   4.269%   $44.2622   $44.26   $44.25   $44.30  
  Purchase #5 $197.78   4.636%   $206.9491   $206.95   $206.95   $206.90  
  Purchase #6 $125.89   11.183%   $139.9683   $139.97   $139.95   $140.00  
  Purchase #7 $244.46   8.866%   $266.1338   $266.13   $266.15   $266.10  
  7 purchase totals = $991.19       $1,063.4116   $1,063.41   $1,063.40   $1,063.40