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	$38.71	7.324%	$41.5451	$41.55	$41.55	$41.50
Purchase #2	$27.89	6.666%	$29.7491	$29.75	$29.75	$29.70
Purchase #3	$31.49	6.813%	$33.6354	$33.64	$33.65	$33.60
Purchase #4	$230.92	10.428%	$255.0003	$255.00	$255.00	$255.00
Purchase #5	$9.61	5.707%	$10.1584	$10.16	$10.15	$10.20
Purchase #6	$55.71	9.150%	$60.8075	$60.81	$60.80	$60.80
Purchase #7	$196.90	13.140%	$222.7727	$222.77	$222.75	$222.80
7 purchase totals =	$591.23		$653.6685	$653.68	$653.65	$653.60