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	$95.72	13.159%	$108.3158	$108.32	$108.30	$108.30
Purchase #2	$104.65	6.126%	$111.0609	$111.06	$111.05	$111.10
Purchase #3	$80.39	8.635%	$87.3317	$87.33	$87.35	$87.30
Purchase #4	$204.29	7.411%	$219.4299	$219.43	$219.45	$219.40
Purchase #5	$117.74	13.134%	$133.204	$133.20	$133.20	$133.20
Purchase #6	$65.49	10.797%	$72.561	$72.56	$72.55	$72.60
Purchase #7	$181.39	3.773%	$188.2338	$188.23	$188.25	$188.20
7 purchase totals =	$849.67		$920.1371	$920.13	$920.15	$920.10