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	$172.57	4.105%	$179.654	$179.65	$179.65	$179.70
Purchase #2	$243.37	4.295%	$253.8227	$253.82	$253.80	$253.80
Purchase #3	$149.46	9.265%	$163.3075	$163.31	$163.30	$163.30
Purchase #4	$41.29	10.164%	$45.4867	$45.49	$45.50	$45.50
Purchase #5	$92.57	8.792%	$100.7088	$100.71	$100.70	$100.70
Purchase #6	$88.67	13.111%	$100.2955	$100.30	$100.30	$100.30
Purchase #7	$52.27	5.837%	$55.321	$55.32	$55.30	$55.30
7 purchase totals =	$840.20		$898.5962	$898.60	$898.55	$898.60