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	$138.43	3.238%	$142.9124	$142.91	$142.90	$142.90
Purchase #2	$86.63	6.524%	$92.2817	$92.28	$92.30	$92.30
Purchase #3	$79.65	10.531%	$88.0379	$88.04	$88.05	$88.00
Purchase #4	$168.27	12.832%	$189.8624	$189.86	$189.85	$189.90
Purchase #5	$122.68	3.680%	$127.1946	$127.19	$127.20	$127.20
Purchase #6	$13.65	4.275%	$14.2335	$14.23	$14.25	$14.20
Purchase #7	$54.43	8.519%	$59.0669	$59.07	$59.05	$59.10
7 purchase totals =	$663.74		$713.5894	$713.58	$713.60	$713.60