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	$104.65	11.841%	$117.0416	$117.04	$117.05	$117.00
Purchase #2	$37.27	12.195%	$41.8151	$41.82	$41.80	$41.80
Purchase #3	$35.98	13.443%	$40.8168	$40.82	$40.80	$40.80
Purchase #4	$104.77	7.271%	$112.3878	$112.39	$112.40	$112.40
Purchase #5	$212.98	8.422%	$230.9172	$230.92	$230.90	$230.90
Purchase #6	$247.50	13.741%	$281.509	$281.51	$281.50	$281.50
Purchase #7	$42.41	6.781%	$45.2858	$45.29	$45.30	$45.30
7 purchase totals =	$785.56		$869.7733	$869.79	$869.75	$869.70