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	$123.93	5.173%	$130.3409	$130.34	$130.35	$130.30
Purchase #2	$113.67	12.103%	$127.4275	$127.43	$127.45	$127.40
Purchase #3	$20.87	11.672%	$23.3059	$23.31	$23.30	$23.30
Purchase #4	$39.85	6.270%	$42.3486	$42.35	$42.35	$42.30
Purchase #5	$111.51	11.307%	$124.1184	$124.12	$124.10	$124.10
Purchase #6	$143.31	10.707%	$158.6542	$158.65	$158.65	$158.70
Purchase #7	$235.55	9.261%	$257.3643	$257.36	$257.35	$257.40
7 purchase totals =	$788.69		$863.5598	$863.56	$863.55	$863.50