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	$90.39	13.156%	$102.2817	$102.28	$102.30	$102.30
Purchase #2	$13.77	13.835%	$15.6751	$15.68	$15.70	$15.70
Purchase #3	$42.33	4.812%	$44.3669	$44.37	$44.35	$44.40
Purchase #4	$142.98	7.111%	$153.1473	$153.15	$153.15	$153.10
Purchase #5	$205.43	8.292%	$222.4643	$222.46	$222.45	$222.50
Purchase #6	$218.62	13.571%	$248.2889	$248.29	$248.30	$248.30
Purchase #7	$172.93	11.276%	$192.4296	$192.43	$192.45	$192.40
7 purchase totals =	$886.45		$978.6538	$978.66	$978.70	$978.70