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	$53.28	8.131%	$57.6122	$57.61	$57.60	$57.60
Purchase #2	$130.77	13.663%	$148.6371	$148.64	$148.65	$148.60
Purchase #3	$108.87	3.696%	$112.8938	$112.89	$112.90	$112.90
Purchase #4	$66.52	9.464%	$72.8155	$72.82	$72.80	$72.80
Purchase #5	$133.47	9.352%	$145.9521	$145.95	$145.95	$146.00
Purchase #6	$132.28	3.313%	$136.6624	$136.66	$136.65	$136.70
Purchase #7	$149.59	5.440%	$157.7277	$157.73	$157.75	$157.70
7 purchase totals =	$774.78		$832.3008	$832.30	$832.30	$832.30