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	$111.89	8.452%	$121.3469	$121.35	$121.35	$121.30
Purchase #2	$142.52	5.225%	$149.9667	$149.97	$149.95	$150.00
Purchase #3	$109.64	13.236%	$124.152	$124.15	$124.15	$124.20
Purchase #4	$48.48	12.671%	$54.6229	$54.62	$54.60	$54.60
Purchase #5	$196.25	6.817%	$209.6284	$209.63	$209.65	$209.60
Purchase #6	$99.55	11.540%	$111.0381	$111.04	$111.05	$111.00
Purchase #7	$161.38	7.504%	$173.49	$173.49	$173.50	$173.50
7 purchase totals =	$869.71		$944.2450	$944.25	$944.25	$944.20