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	$213.77	13.402%	$242.4195	$242.42	$242.40	$242.40
Purchase #2	$193.40	9.265%	$211.3185	$211.32	$211.30	$211.30
Purchase #3	$66.35	6.752%	$70.83	$70.83	$70.85	$70.80
Purchase #4	$172.95	4.322%	$180.4249	$180.42	$180.40	$180.40
Purchase #5	$89.65	11.161%	$99.6558	$99.66	$99.65	$99.70
Purchase #6	$17.94	8.314%	$19.4315	$19.43	$19.45	$19.40
Purchase #7	$148.37	12.306%	$166.6284	$166.63	$166.65	$166.60
7 purchase totals =	$902.43		$990.7086	$990.71	$990.70	$990.60