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	$50.72	8.104%	$54.8303	$54.83	$54.85	$54.80
Purchase #2	$134.78	10.682%	$149.1772	$149.18	$149.20	$149.20
Purchase #3	$149.53	7.105%	$160.1541	$160.15	$160.15	$160.20
Purchase #4	$154.30	5.204%	$162.3298	$162.33	$162.35	$162.30
Purchase #5	$33.87	11.487%	$37.7606	$37.76	$37.75	$37.80
Purchase #6	$175.72	7.202%	$188.3754	$188.38	$188.40	$188.40
Purchase #7	$64.56	4.131%	$67.227	$67.23	$67.25	$67.20
7 purchase totals =	$763.48		$819.8544	$819.86	$819.95	$819.90