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	$19.42	13.732%	$22.0868	$22.09	$22.10	$22.10
Purchase #2	$124.84	11.737%	$139.4925	$139.49	$139.50	$139.50
Purchase #3	$227.82	7.285%	$244.4167	$244.42	$244.40	$244.40
Purchase #4	$129.71	9.621%	$142.1894	$142.19	$142.20	$142.20
Purchase #5	$166.91	13.770%	$189.8935	$189.89	$189.90	$189.90
Purchase #6	$50.29	9.413%	$55.0238	$55.02	$55.00	$55.00
Purchase #7	$228.90	4.236%	$238.5962	$238.60	$238.60	$238.60
7 purchase totals =	$947.89		$1,031.6989	$1,031.70	$1,031.70	$1,031.70