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	$29.78	12.773%	$33.5838	$33.58	$33.60	$33.60
Purchase #2	$92.78	9.178%	$101.2953	$101.30	$101.30	$101.30
Purchase #3	$48.51	9.821%	$53.2742	$53.27	$53.25	$53.30
Purchase #4	$176.71	11.258%	$196.604	$196.60	$196.60	$196.60
Purchase #5	$115.99	9.834%	$127.3965	$127.40	$127.40	$127.40
Purchase #6	$117.54	10.574%	$129.9687	$129.97	$129.95	$130.00
Purchase #7	$243.39	8.829%	$264.8789	$264.88	$264.90	$264.90
7 purchase totals =	$824.70		$907.0014	$907.00	$907.00	$907.10