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	$87.26	4.113%	$90.849	$90.85	$90.85	$90.80
Purchase #2	$71.56	12.539%	$80.5329	$80.53	$80.55	$80.50
Purchase #3	$43.90	10.696%	$48.5955	$48.60	$48.60	$48.60
Purchase #4	$206.91	13.840%	$235.5463	$235.55	$235.55	$235.50
Purchase #5	$108.54	12.569%	$122.1824	$122.18	$122.20	$122.20
Purchase #6	$62.99	5.283%	$66.3178	$66.32	$66.30	$66.30
Purchase #7	$85.47	12.172%	$95.8734	$95.87	$95.85	$95.90
7 purchase totals =	$666.63		$739.8973	$739.90	$739.90	$739.80