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	$39.70	7.367%	$42.6247	$42.62	$42.60	$42.60
Purchase #2	$203.51	13.741%	$231.4743	$231.47	$231.45	$231.50
Purchase #3	$129.64	11.520%	$144.5745	$144.57	$144.55	$144.60
Purchase #4	$215.72	7.697%	$232.324	$232.32	$232.30	$232.30
Purchase #5	$57.55	7.806%	$62.0424	$62.04	$62.05	$62.00
Purchase #6	$72.81	9.169%	$79.4859	$79.49	$79.50	$79.50
Purchase #7	$50.90	5.322%	$53.6089	$53.61	$53.60	$53.60
7 purchase totals =	$769.83		$846.1347	$846.12	$846.05	$846.10