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	$18.46	5.108%	$19.4029	$19.40	$19.40	$19.40
Purchase #2	$180.37	13.806%	$205.2719	$205.27	$205.25	$205.30
Purchase #3	$58.46	13.129%	$66.1352	$66.14	$66.15	$66.10
Purchase #4	$242.51	4.611%	$253.6921	$253.69	$253.70	$253.70
Purchase #5	$70.39	4.453%	$73.5245	$73.52	$73.50	$73.50
Purchase #6	$56.48	4.741%	$59.1577	$59.16	$59.15	$59.20
Purchase #7	$108.82	13.289%	$123.2811	$123.28	$123.30	$123.30
7 purchase totals =	$735.49		$800.4654	$800.46	$800.45	$800.50