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 $198.63   4.315%   $207.2009   $207.20   $207.20   $207.20  
  Purchase #2 $54.84   10.801%   $60.7633   $60.76   $60.75   $60.80  
  Purchase #3 $68.47   7.283%   $73.4567   $73.46   $73.45   $73.50  
  Purchase #4 $44.76   4.745%   $46.8839   $46.88   $46.90   $46.90  
  Purchase #5 $90.88   6.634%   $96.909   $96.91   $96.90   $96.90  
  Purchase #6 $211.57   3.636%   $219.2627   $219.26   $219.25   $219.30  
  Purchase #7 $221.68   12.302%   $248.9511   $248.95   $248.95   $249.00  
  7 purchase totals = $890.83       $953.4276   $953.42   $953.40   $953.60