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	$74.68	6.486%	$79.5237	$79.52	$79.50	$79.50
Purchase #2	$176.76	12.663%	$199.1431	$199.14	$199.15	$199.10
Purchase #3	$152.51	13.606%	$173.2605	$173.26	$173.25	$173.30
Purchase #4	$184.34	13.725%	$209.6407	$209.64	$209.65	$209.60
Purchase #5	$150.45	10.286%	$165.9253	$165.93	$165.95	$165.90
Purchase #6	$43.59	10.456%	$48.1478	$48.15	$48.15	$48.10
Purchase #7	$155.87	10.268%	$171.8747	$171.87	$171.85	$171.90
7 purchase totals =	$938.20		$1,047.5158	$1,047.51	$1,047.50	$1,047.40