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	$235.83	13.523%	$267.7213	$267.72	$267.70	$267.70
Purchase #2	$243.89	9.407%	$266.8327	$266.83	$266.85	$266.80
Purchase #3	$20.28	10.718%	$22.4536	$22.45	$22.45	$22.50
Purchase #4	$132.83	7.163%	$142.3446	$142.34	$142.35	$142.30
Purchase #5	$35.77	6.707%	$38.1691	$38.17	$38.15	$38.20
Purchase #6	$149.63	4.317%	$156.0895	$156.09	$156.10	$156.10
Purchase #7	$72.35	13.569%	$82.1672	$82.17	$82.15	$82.20
7 purchase totals =	$890.58		$975.7780	$975.77	$975.75	$975.80