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	$135.51	4.402%	$141.4752	$141.48	$141.50	$141.50
Purchase #2	$117.52	3.720%	$121.8917	$121.89	$121.90	$121.90
Purchase #3	$57.88	8.444%	$62.7674	$62.77	$62.75	$62.80
Purchase #4	$40.55	11.361%	$45.1569	$45.16	$45.15	$45.20
Purchase #5	$99.62	4.332%	$103.9355	$103.94	$103.95	$103.90
Purchase #6	$166.37	4.293%	$173.5123	$173.51	$173.50	$173.50
Purchase #7	$127.74	10.203%	$140.7733	$140.77	$140.75	$140.80
7 purchase totals =	$745.19		$789.5123	$789.52	$789.50	$789.60