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	$33.66	10.522%	$37.2017	$37.20	$37.20	$37.20
Purchase #2	$215.88	6.688%	$230.3181	$230.32	$230.30	$230.30
Purchase #3	$164.93	4.312%	$172.0418	$172.04	$172.05	$172.00
Purchase #4	$54.38	9.748%	$59.681	$59.68	$59.70	$59.70
Purchase #5	$108.40	4.165%	$112.9149	$112.91	$112.90	$112.90
Purchase #6	$143.96	6.799%	$153.7478	$153.75	$153.75	$153.70
Purchase #7	$175.39	5.312%	$184.7067	$184.71	$184.70	$184.70
7 purchase totals =	$896.60		$950.6120	$950.61	$950.60	$950.50