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	$146.43	8.388%	$158.7125	$158.71	$158.70	$158.70
Purchase #2	$52.76	13.470%	$59.8668	$59.87	$59.85	$59.90
Purchase #3	$80.77	10.608%	$89.3381	$89.34	$89.35	$89.30
Purchase #4	$147.28	13.286%	$166.8476	$166.85	$166.85	$166.80
Purchase #5	$30.27	5.342%	$31.887	$31.89	$31.90	$31.90
Purchase #6	$246.77	12.487%	$277.5842	$277.58	$277.60	$277.60
Purchase #7	$219.77	6.459%	$233.9649	$233.96	$233.95	$234.00
7 purchase totals =	$924.05		$1,018.2011	$1,018.20	$1,018.20	$1,018.20