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	$91.86	9.540%	$100.6234	$100.62	$100.60	$100.60
Purchase #2	$105.77	5.347%	$111.4255	$111.43	$111.45	$111.40
Purchase #3	$39.54	8.267%	$42.8088	$42.81	$42.80	$42.80
Purchase #4	$139.32	13.301%	$157.851	$157.85	$157.85	$157.90
Purchase #5	$69.65	4.579%	$72.8393	$72.84	$72.85	$72.80
Purchase #6	$92.49	9.581%	$101.3515	$101.35	$101.35	$101.40
Purchase #7	$74.96	11.809%	$83.812	$83.81	$83.80	$83.80
7 purchase totals =	$613.59		$670.7115	$670.71	$670.70	$670.70