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	$135.67	5.842%	$143.5958	$143.60	$143.60	$143.60
Purchase #2	$134.91	3.729%	$139.9408	$139.94	$139.95	$139.90
Purchase #3	$203.85	9.393%	$222.9976	$223.00	$223.00	$223.00
Purchase #4	$92.52	11.490%	$103.1505	$103.15	$103.15	$103.20
Purchase #5	$69.77	9.323%	$76.2747	$76.27	$76.25	$76.30
Purchase #6	$10.62	13.649%	$12.0695	$12.07	$12.05	$12.10
Purchase #7	$59.80	4.658%	$62.5855	$62.59	$62.60	$62.60
7 purchase totals =	$707.14		$760.6144	$760.62	$760.60	$760.70