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	$238.33	13.829%	$271.2887	$271.29	$271.30	$271.30
Purchase #2	$125.62	9.281%	$137.2788	$137.28	$137.30	$137.30
Purchase #3	$125.46	8.480%	$136.099	$136.10	$136.10	$136.10
Purchase #4	$50.41	7.244%	$54.0617	$54.06	$54.05	$54.10
Purchase #5	$57.29	11.407%	$63.8251	$63.83	$63.85	$63.80
Purchase #6	$222.78	13.596%	$253.0692	$253.07	$253.05	$253.10
Purchase #7	$100.51	12.258%	$112.8305	$112.83	$112.85	$112.80
7 purchase totals =	$920.40		$1,028.4530	$1,028.46	$1,028.50	$1,028.50