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	$85.66	7.580%	$92.153	$92.15	$92.15	$92.20
Purchase #2	$128.85	12.603%	$145.089	$145.09	$145.10	$145.10
Purchase #3	$220.62	8.223%	$238.7616	$238.76	$238.75	$238.80
Purchase #4	$40.53	12.483%	$45.5894	$45.59	$45.60	$45.60
Purchase #5	$243.30	6.622%	$259.4113	$259.41	$259.40	$259.40
Purchase #6	$12.51	12.427%	$14.0646	$14.06	$14.05	$14.10
Purchase #7	$51.89	5.381%	$54.6822	$54.68	$54.70	$54.70
7 purchase totals =	$783.36		$849.7511	$849.74	$849.75	$849.90