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	$58.61	13.152%	$66.3184	$66.32	$66.30	$66.30
Purchase #2	$120.79	5.720%	$127.6992	$127.70	$127.70	$127.70
Purchase #3	$103.52	7.761%	$111.5542	$111.55	$111.55	$111.60
Purchase #4	$49.49	11.172%	$55.019	$55.02	$55.00	$55.00
Purchase #5	$29.54	13.228%	$33.4476	$33.45	$33.45	$33.40
Purchase #6	$220.91	7.634%	$237.7743	$237.77	$237.75	$237.80
Purchase #7	$104.34	3.723%	$108.2246	$108.22	$108.20	$108.20
7 purchase totals =	$687.20		$740.0373	$740.03	$739.95	$740.00