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	$182.25	5.500%	$192.2738	$192.27	$192.25	$192.30
Purchase #2	$36.72	9.404%	$40.1731	$40.17	$40.15	$40.20
Purchase #3	$70.41	9.536%	$77.1243	$77.12	$77.10	$77.10
Purchase #4	$241.51	5.700%	$255.2761	$255.28	$255.30	$255.30
Purchase #5	$124.29	3.330%	$128.4289	$128.43	$128.45	$128.40
Purchase #6	$18.37	13.836%	$20.9117	$20.91	$20.90	$20.90
Purchase #7	$116.28	9.457%	$127.2766	$127.28	$127.30	$127.30
7 purchase totals =	$789.83		$841.4645	$841.46	$841.45	$841.50