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	$90.58	10.579%	$100.1625	$100.16	$100.15	$100.20
Purchase #2	$81.69	4.239%	$85.1528	$85.15	$85.15	$85.20
Purchase #3	$46.50	7.824%	$50.1382	$50.14	$50.15	$50.10
Purchase #4	$21.35	5.166%	$22.4529	$22.45	$22.45	$22.50
Purchase #5	$129.37	4.249%	$134.8669	$134.87	$134.85	$134.90
Purchase #6	$53.69	7.440%	$57.6845	$57.68	$57.70	$57.70
Purchase #7	$54.79	4.618%	$57.3202	$57.32	$57.30	$57.30
7 purchase totals =	$477.97		$507.7780	$507.77	$507.75	$507.90