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	$39.30	10.743%	$43.522	$43.52	$43.50	$43.50
Purchase #2	$243.28	5.561%	$256.8088	$256.81	$256.80	$256.80
Purchase #3	$48.81	3.638%	$50.5857	$50.59	$50.60	$50.60
Purchase #4	$176.48	5.685%	$186.5129	$186.51	$186.50	$186.50
Purchase #5	$165.69	13.502%	$188.0615	$188.06	$188.05	$188.10
Purchase #6	$98.42	13.719%	$111.9222	$111.92	$111.90	$111.90
Purchase #7	$246.39	13.573%	$279.8325	$279.83	$279.85	$279.80
7 purchase totals =	$1,018.37		$1,117.2456	$1,117.24	$1,117.20	$1,117.20