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	$83.74	7.586%	$90.0925	$90.09	$90.10	$90.10
Purchase #2	$161.82	7.104%	$173.3157	$173.32	$173.30	$173.30
Purchase #3	$48.26	10.323%	$53.2419	$53.24	$53.25	$53.20
Purchase #4	$142.54	7.297%	$152.9411	$152.94	$152.95	$152.90
Purchase #5	$114.58	11.493%	$127.7487	$127.75	$127.75	$127.70
Purchase #6	$179.39	9.643%	$196.6886	$196.69	$196.70	$196.70
Purchase #7	$36.33	7.796%	$39.1623	$39.16	$39.15	$39.20
7 purchase totals =	$766.66		$833.1908	$833.19	$833.20	$833.10