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	$21.86	4.702%	$22.8879	$22.89	$22.90	$22.90
Purchase #2	$132.77	10.155%	$146.2528	$146.25	$146.25	$146.30
Purchase #3	$177.51	7.644%	$191.0789	$191.08	$191.10	$191.10
Purchase #4	$85.72	10.700%	$94.892	$94.89	$94.90	$94.90
Purchase #5	$212.60	8.462%	$230.5902	$230.59	$230.60	$230.60
Purchase #6	$65.88	10.146%	$72.5642	$72.56	$72.55	$72.60
Purchase #7	$183.72	13.163%	$207.9031	$207.90	$207.90	$207.90
7 purchase totals =	$880.06		$966.1691	$966.16	$966.20	$966.30