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	$37.67	12.722%	$42.4624	$42.46	$42.45	$42.50
Purchase #2	$141.38	4.739%	$148.08	$148.08	$148.10	$148.10
Purchase #3	$146.61	4.868%	$153.747	$153.75	$153.75	$153.70
Purchase #4	$201.27	10.591%	$222.5865	$222.59	$222.60	$222.60
Purchase #5	$19.68	6.657%	$20.9901	$20.99	$21.00	$21.00
Purchase #6	$79.71	3.476%	$82.4807	$82.48	$82.50	$82.50
Purchase #7	$43.75	13.332%	$49.5828	$49.58	$49.60	$49.60
7 purchase totals =	$670.07		$719.9295	$719.93	$720.00	$720.00