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	$109.79	6.410%	$116.8275	$116.83	$116.85	$116.80
Purchase #2	$54.38	8.188%	$58.8326	$58.83	$58.85	$58.80
Purchase #3	$58.78	4.578%	$61.4709	$61.47	$61.45	$61.50
Purchase #4	$20.94	6.113%	$22.2201	$22.22	$22.20	$22.20
Purchase #5	$136.44	5.848%	$144.419	$144.42	$144.40	$144.40
Purchase #6	$88.35	13.826%	$100.5653	$100.57	$100.55	$100.60
Purchase #7	$214.54	10.535%	$237.1418	$237.14	$237.15	$237.10
7 purchase totals =	$683.22		$741.4772	$741.48	$741.45	$741.40