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	$10.99	9.238%	$12.0053	$12.01	$12.00	$12.00
Purchase #2	$175.49	7.176%	$188.0832	$188.08	$188.10	$188.10
Purchase #3	$227.61	8.809%	$247.6602	$247.66	$247.65	$247.70
Purchase #4	$166.63	11.383%	$185.5975	$185.60	$185.60	$185.60
Purchase #5	$114.30	13.209%	$129.3979	$129.40	$129.40	$129.40
Purchase #6	$76.26	12.146%	$85.5225	$85.52	$85.50	$85.50
Purchase #7	$229.27	3.864%	$238.129	$238.13	$238.15	$238.10
7 purchase totals =	$1,000.55		$1,086.3956	$1,086.40	$1,086.40	$1,086.40