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	$60.80	8.721%	$66.1024	$66.10	$66.10	$66.10
Purchase #2	$193.77	12.767%	$218.5086	$218.51	$218.50	$218.50
Purchase #3	$82.50	9.620%	$90.4365	$90.44	$90.45	$90.40
Purchase #4	$242.30	5.350%	$255.2631	$255.26	$255.25	$255.30
Purchase #5	$195.82	4.286%	$204.2128	$204.21	$204.20	$204.20
Purchase #6	$235.39	8.846%	$256.2126	$256.21	$256.20	$256.20
Purchase #7	$11.81	10.297%	$13.0261	$13.03	$13.05	$13.00
7 purchase totals =	$1,022.39		$1,103.7621	$1,103.76	$1,103.75	$1,103.70