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	$95.35	4.675%	$99.8076	$99.81	$99.80	$99.80
Purchase #2	$186.39	11.242%	$207.344	$207.34	$207.35	$207.30
Purchase #3	$118.53	4.203%	$123.5118	$123.51	$123.50	$123.50
Purchase #4	$250.47	11.511%	$279.3016	$279.30	$279.30	$279.30
Purchase #5	$19.75	8.670%	$21.4623	$21.46	$21.45	$21.50
Purchase #6	$122.60	3.679%	$127.1105	$127.11	$127.10	$127.10
Purchase #7	$61.27	12.660%	$69.0268	$69.03	$69.05	$69.00
7 purchase totals =	$854.36		$927.5646	$927.56	$927.55	$927.50