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	$55.39	5.166%	$58.2514	$58.25	$58.25	$58.30
Purchase #2	$54.28	13.543%	$61.6311	$61.63	$61.65	$61.60
Purchase #3	$104.59	4.503%	$109.2997	$109.30	$109.30	$109.30
Purchase #4	$21.97	11.218%	$24.4346	$24.43	$24.45	$24.40
Purchase #5	$153.52	11.328%	$170.9107	$170.91	$170.90	$170.90
Purchase #6	$217.51	7.420%	$233.6492	$233.65	$233.65	$233.60
Purchase #7	$139.75	3.269%	$144.3184	$144.32	$144.30	$144.30
7 purchase totals =	$747.01		$802.4951	$802.49	$802.50	$802.40