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	$143.97	5.316%	$151.6234	$151.62	$151.60	$151.60
Purchase #2	$40.27	12.381%	$45.2558	$45.26	$45.25	$45.30
Purchase #3	$234.29	13.760%	$266.5283	$266.53	$266.55	$266.50
Purchase #4	$99.54	6.607%	$106.1166	$106.12	$106.10	$106.10
Purchase #5	$183.56	4.271%	$191.3998	$191.40	$191.40	$191.40
Purchase #6	$182.28	6.356%	$193.8657	$193.87	$193.85	$193.90
Purchase #7	$135.91	7.532%	$146.1467	$146.15	$146.15	$146.10
7 purchase totals =	$1,019.82		$1,100.9363	$1,100.95	$1,100.90	$1,100.90