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	$158.88	9.773%	$174.4073	$174.41	$174.40	$174.40
Purchase #2	$58.89	10.192%	$64.8921	$64.89	$64.90	$64.90
Purchase #3	$45.49	8.283%	$49.2579	$49.26	$49.25	$49.30
Purchase #4	$157.72	5.325%	$166.1186	$166.12	$166.10	$166.10
Purchase #5	$122.34	4.409%	$127.734	$127.73	$127.75	$127.70
Purchase #6	$19.94	3.388%	$20.6156	$20.62	$20.60	$20.60
Purchase #7	$175.62	7.199%	$188.2629	$188.26	$188.25	$188.30
7 purchase totals =	$738.88		$791.2884	$791.29	$791.25	$791.30