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	$139.43	6.289%	$148.1988	$148.20	$148.20	$148.20
Purchase #2	$97.46	8.193%	$105.4449	$105.44	$105.45	$105.40
Purchase #3	$57.88	13.503%	$65.6955	$65.70	$65.70	$65.70
Purchase #4	$105.88	3.492%	$109.5773	$109.58	$109.60	$109.60
Purchase #5	$139.62	7.766%	$150.4629	$150.46	$150.45	$150.50
Purchase #6	$232.38	6.359%	$247.157	$247.16	$247.15	$247.20
Purchase #7	$127.31	4.795%	$133.4145	$133.41	$133.40	$133.40
7 purchase totals =	$899.96		$959.9509	$959.95	$959.95	$960.00