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	$53.51	6.376%	$56.9218	$56.92	$56.90	$56.90
Purchase #2	$61.75	9.380%	$67.5422	$67.54	$67.55	$67.50
Purchase #3	$147.56	13.202%	$167.0409	$167.04	$167.05	$167.00
Purchase #4	$30.61	8.241%	$33.1326	$33.13	$33.15	$33.10
Purchase #5	$214.83	9.287%	$234.7813	$234.78	$234.80	$234.80
Purchase #6	$83.37	7.612%	$89.7161	$89.72	$89.70	$89.70
Purchase #7	$231.85	6.653%	$247.275	$247.28	$247.30	$247.30
7 purchase totals =	$823.48		$896.4099	$896.41	$896.45	$896.30