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	$149.86	6.435%	$159.5035	$159.50	$159.50	$159.50
Purchase #2	$166.98	8.111%	$180.5237	$180.52	$180.50	$180.50
Purchase #3	$225.55	10.157%	$248.4591	$248.46	$248.45	$248.50
Purchase #4	$145.77	13.703%	$165.7449	$165.74	$165.75	$165.70
Purchase #5	$169.28	5.245%	$178.1587	$178.16	$178.15	$178.20
Purchase #6	$74.61	10.811%	$82.6761	$82.68	$82.70	$82.70
Purchase #7	$44.89	7.660%	$48.3286	$48.33	$48.35	$48.30
7 purchase totals =	$976.94		$1,063.3946	$1,063.39	$1,063.40	$1,063.40