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	$43.51	13.794%	$49.5118	$49.51	$49.50	$49.50
Purchase #2	$146.68	10.344%	$161.8526	$161.85	$161.85	$161.90
Purchase #3	$19.43	10.675%	$21.5042	$21.50	$21.50	$21.50
Purchase #4	$130.48	10.707%	$144.4505	$144.45	$144.45	$144.50
Purchase #5	$37.58	4.749%	$39.3647	$39.36	$39.35	$39.40
Purchase #6	$220.34	13.111%	$249.2288	$249.23	$249.25	$249.20
Purchase #7	$153.40	4.194%	$159.8336	$159.83	$159.85	$159.80
7 purchase totals =	$751.42		$825.7462	$825.73	$825.75	$825.80