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	$17.96	13.408%	$20.3681	$20.37	$20.35	$20.40
Purchase #2	$29.25	13.823%	$33.2932	$33.29	$33.30	$33.30
Purchase #3	$56.66	4.518%	$59.2199	$59.22	$59.20	$59.20
Purchase #4	$137.85	12.415%	$154.9641	$154.96	$154.95	$155.00
Purchase #5	$157.62	8.328%	$170.7466	$170.75	$170.75	$170.70
Purchase #6	$211.55	6.152%	$224.5646	$224.56	$224.55	$224.60
Purchase #7	$18.51	10.223%	$20.4023	$20.40	$20.40	$20.40
7 purchase totals =	$629.40		$683.5588	$683.55	$683.50	$683.60