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	$31.27	3.713%	$32.4311	$32.43	$32.45	$32.40
Purchase #2	$105.65	8.305%	$114.4242	$114.42	$114.40	$114.40
Purchase #3	$156.80	9.777%	$172.1303	$172.13	$172.15	$172.10
Purchase #4	$102.56	10.231%	$113.0529	$113.05	$113.05	$113.10
Purchase #5	$61.37	8.553%	$66.619	$66.62	$66.60	$66.60
Purchase #6	$82.51	9.245%	$90.138	$90.14	$90.15	$90.10
Purchase #7	$166.35	9.243%	$181.7257	$181.73	$181.75	$181.70
7 purchase totals =	$706.51		$770.5212	$770.52	$770.55	$770.40