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	$250.80	11.341%	$279.2432	$279.24	$279.25	$279.20
Purchase #2	$52.49	10.175%	$57.8309	$57.83	$57.85	$57.80
Purchase #3	$159.52	10.251%	$175.8724	$175.87	$175.85	$175.90
Purchase #4	$165.91	4.132%	$172.7654	$172.77	$172.75	$172.80
Purchase #5	$5.44	11.125%	$6.0452	$6.05	$6.05	$6.00
Purchase #6	$165.90	4.806%	$173.8732	$173.87	$173.85	$173.90
Purchase #7	$148.83	11.717%	$166.2684	$166.27	$166.25	$166.30
7 purchase totals =	$948.89		$1,031.8987	$1,031.90	$1,031.85	$1,031.90