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	$57.52	7.383%	$61.7667	$61.77	$61.75	$61.80
Purchase #2	$53.30	5.605%	$56.2875	$56.29	$56.30	$56.30
Purchase #3	$110.60	6.862%	$118.1894	$118.19	$118.20	$118.20
Purchase #4	$42.54	7.765%	$45.8432	$45.84	$45.85	$45.80
Purchase #5	$59.41	11.812%	$66.4275	$66.43	$66.45	$66.40
Purchase #6	$247.79	12.714%	$279.294	$279.29	$279.30	$279.30
Purchase #7	$6.27	5.720%	$6.6286	$6.63	$6.65	$6.60
7 purchase totals =	$577.43		$634.4369	$634.44	$634.50	$634.40