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	$20.44	6.223%	$21.712	$21.71	$21.70	$21.70
Purchase #2	$49.96	4.562%	$52.2392	$52.24	$52.25	$52.20
Purchase #3	$117.35	5.339%	$123.6153	$123.62	$123.60	$123.60
Purchase #4	$220.79	9.784%	$242.3921	$242.39	$242.40	$242.40
Purchase #5	$137.75	7.663%	$148.3058	$148.31	$148.30	$148.30
Purchase #6	$152.63	6.192%	$162.0808	$162.08	$162.10	$162.10
Purchase #7	$28.60	13.571%	$32.4813	$32.48	$32.50	$32.50
7 purchase totals =	$727.52		$782.8265	$782.83	$782.85	$782.80