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	$135.25	13.389%	$153.3586	$153.36	$153.35	$153.40
Purchase #2	$98.38	10.141%	$108.3567	$108.36	$108.35	$108.40
Purchase #3	$42.42	6.451%	$45.1565	$45.16	$45.15	$45.20
Purchase #4	$54.81	4.630%	$57.3477	$57.35	$57.35	$57.30
Purchase #5	$6.87	4.768%	$7.1976	$7.20	$7.20	$7.20
Purchase #6	$56.78	8.731%	$61.7375	$61.74	$61.75	$61.70
Purchase #7	$85.61	4.554%	$89.5087	$89.51	$89.50	$89.50
7 purchase totals =	$480.12		$522.6633	$522.68	$522.65	$522.70