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 $69.32   5.675%   $73.2539   $73.25   $73.25   $73.30  
  Purchase #2 $237.79   3.847%   $246.9378   $246.94   $246.95   $246.90  
  Purchase #3 $135.63   4.321%   $141.4906   $141.49   $141.50   $141.50  
  Purchase #4 $119.77   3.710%   $124.2135   $124.21   $124.20   $124.20  
  Purchase #5 $184.63   4.142%   $192.2774   $192.28   $192.30   $192.30  
  Purchase #6 $74.37   9.727%   $81.604   $81.60   $81.60   $81.60  
  Purchase #7 $49.26   8.305%   $53.351   $53.35   $53.35   $53.40  
  7 purchase totals = $870.77       $913.1282   $913.12   $913.15   $913.20