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	$115.71	12.705%	$130.411	$130.41	$130.40	$130.40
Purchase #2	$29.34	10.130%	$32.3121	$32.31	$32.30	$32.30
Purchase #3	$173.64	3.636%	$179.9536	$179.95	$179.95	$180.00
Purchase #4	$167.49	11.490%	$186.7346	$186.73	$186.75	$186.70
Purchase #5	$152.76	13.754%	$173.7706	$173.77	$173.75	$173.80
Purchase #6	$127.28	13.343%	$144.263	$144.26	$144.25	$144.30
Purchase #7	$141.74	7.470%	$152.328	$152.33	$152.35	$152.30
7 purchase totals =	$907.96		$999.7729	$999.76	$999.75	$999.80