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	$234.86	10.838%	$260.3141	$260.31	$260.30	$260.30
Purchase #2	$175.97	9.442%	$192.5851	$192.59	$192.60	$192.60
Purchase #3	$42.77	5.342%	$45.0548	$45.05	$45.05	$45.10
Purchase #4	$137.59	13.713%	$156.4577	$156.46	$156.45	$156.50
Purchase #5	$60.32	3.698%	$62.5506	$62.55	$62.55	$62.60
Purchase #6	$139.46	5.151%	$146.6436	$146.64	$146.65	$146.60
Purchase #7	$35.66	10.795%	$39.5095	$39.51	$39.50	$39.50
7 purchase totals =	$826.63		$903.1154	$903.11	$903.10	$903.20