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	$153.88	12.374%	$172.9211	$172.92	$172.90	$172.90
Purchase #2	$109.72	7.598%	$118.0565	$118.06	$118.05	$118.10
Purchase #3	$140.89	3.215%	$145.4196	$145.42	$145.40	$145.40
Purchase #4	$169.90	5.474%	$179.2003	$179.20	$179.20	$179.20
Purchase #5	$41.29	9.243%	$45.1064	$45.11	$45.10	$45.10
Purchase #6	$19.98	8.537%	$21.6857	$21.69	$21.70	$21.70
Purchase #7	$126.33	4.123%	$131.5386	$131.54	$131.55	$131.50
7 purchase totals =	$761.99		$813.9282	$813.94	$813.90	$813.90