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	$22.76	6.326%	$24.1998	$24.20	$24.20	$24.20
Purchase #2	$68.50	11.815%	$76.5933	$76.59	$76.60	$76.60
Purchase #3	$97.40	8.545%	$105.7228	$105.72	$105.70	$105.70
Purchase #4	$94.76	8.767%	$103.0676	$103.07	$103.05	$103.10
Purchase #5	$200.28	5.136%	$210.5664	$210.57	$210.55	$210.60
Purchase #6	$117.90	8.429%	$127.8378	$127.84	$127.85	$127.80
Purchase #7	$126.59	11.676%	$141.3706	$141.37	$141.35	$141.40
7 purchase totals =	$728.19		$789.3583	$789.36	$789.30	$789.40