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	$80.90	13.257%	$91.6249	$91.62	$91.60	$91.60
Purchase #2	$80.59	11.716%	$90.0319	$90.03	$90.05	$90.00
Purchase #3	$117.85	4.632%	$123.3088	$123.31	$123.30	$123.30
Purchase #4	$83.43	10.815%	$92.453	$92.45	$92.45	$92.50
Purchase #5	$155.76	9.228%	$170.1335	$170.13	$170.15	$170.10
Purchase #6	$134.75	5.202%	$141.7597	$141.76	$141.75	$141.80
Purchase #7	$141.37	8.378%	$153.214	$153.21	$153.20	$153.20
7 purchase totals =	$794.65		$862.5258	$862.51	$862.50	$862.50