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	$34.48	9.635%	$37.8021	$37.80	$37.80	$37.80
Purchase #2	$91.85	6.236%	$97.5778	$97.58	$97.60	$97.60
Purchase #3	$6.98	9.775%	$7.6623	$7.66	$7.65	$7.70
Purchase #4	$111.98	13.778%	$127.4086	$127.41	$127.40	$127.40
Purchase #5	$207.58	7.855%	$223.8854	$223.89	$223.90	$223.90
Purchase #6	$174.82	7.815%	$188.4822	$188.48	$188.50	$188.50
Purchase #7	$107.71	10.780%	$119.3211	$119.32	$119.30	$119.30
7 purchase totals =	$735.40		$802.1395	$802.14	$802.15	$802.20