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	$135.82	13.318%	$153.9085	$153.91	$153.90	$153.90
Purchase #2	$146.96	9.276%	$160.592	$160.59	$160.60	$160.60
Purchase #3	$12.39	10.803%	$13.7285	$13.73	$13.75	$13.70
Purchase #4	$174.77	7.838%	$188.4685	$188.47	$188.45	$188.50
Purchase #5	$248.31	5.580%	$262.1657	$262.17	$262.15	$262.20
Purchase #6	$56.44	4.725%	$59.1068	$59.11	$59.10	$59.10
Purchase #7	$27.94	5.543%	$29.4887	$29.49	$29.50	$29.50
7 purchase totals =	$802.63		$867.4587	$867.47	$867.45	$867.50