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	$249.64	10.251%	$275.2306	$275.23	$275.25	$275.20
Purchase #2	$49.30	8.358%	$53.4205	$53.42	$53.40	$53.40
Purchase #3	$199.68	3.811%	$207.2898	$207.29	$207.30	$207.30
Purchase #4	$175.91	12.712%	$198.2717	$198.27	$198.25	$198.30
Purchase #5	$214.51	7.228%	$230.0148	$230.01	$230.00	$230.00
Purchase #6	$102.89	9.173%	$112.3281	$112.33	$112.35	$112.30
Purchase #7	$90.60	5.521%	$95.602	$95.60	$95.60	$95.60
7 purchase totals =	$1,082.53		$1,172.1575	$1,172.15	$1,172.15	$1,172.10