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	$239.71	3.510%	$248.1238	$248.12	$248.10	$248.10
Purchase #2	$239.74	3.769%	$248.7758	$248.78	$248.80	$248.80
Purchase #3	$151.98	13.282%	$172.166	$172.17	$172.15	$172.20
Purchase #4	$42.63	6.686%	$45.4802	$45.48	$45.50	$45.50
Purchase #5	$17.45	13.521%	$19.8094	$19.81	$19.80	$19.80
Purchase #6	$96.76	4.244%	$100.8665	$100.87	$100.85	$100.90
Purchase #7	$153.77	3.427%	$159.0397	$159.04	$159.05	$159.00
7 purchase totals =	$942.04		$994.2614	$994.27	$994.25	$994.30