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	$154.53	4.522%	$161.5178	$161.52	$161.50	$161.50
Purchase #2	$222.31	4.211%	$231.6715	$231.67	$231.65	$231.70
Purchase #3	$119.85	3.113%	$123.5809	$123.58	$123.60	$123.60
Purchase #4	$10.71	6.205%	$11.3746	$11.37	$11.35	$11.40
Purchase #5	$33.64	13.472%	$38.172	$38.17	$38.15	$38.20
Purchase #6	$13.58	12.119%	$15.2258	$15.23	$15.25	$15.20
Purchase #7	$54.63	11.705%	$61.0244	$61.02	$61.00	$61.00
7 purchase totals =	$609.25		$642.5670	$642.56	$642.50	$642.60