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	$107.55	3.339%	$111.1411	$111.14	$111.15	$111.10
Purchase #2	$74.79	11.567%	$83.441	$83.44	$83.45	$83.40
Purchase #3	$222.83	7.196%	$238.8648	$238.86	$238.85	$238.90
Purchase #4	$34.79	10.333%	$38.3849	$38.38	$38.40	$38.40
Purchase #5	$186.79	13.350%	$211.7265	$211.73	$211.75	$211.70
Purchase #6	$164.82	7.434%	$177.0727	$177.07	$177.05	$177.10
Purchase #7	$111.95	10.206%	$123.3756	$123.38	$123.40	$123.40
7 purchase totals =	$903.52		$984.0066	$984.00	$984.05	$984.00