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	$36.41	12.313%	$40.8932	$40.89	$40.90	$40.90
Purchase #2	$95.98	3.196%	$99.0475	$99.05	$99.05	$99.00
Purchase #3	$224.62	4.522%	$234.7773	$234.78	$234.80	$234.80
Purchase #4	$87.50	13.835%	$99.6056	$99.61	$99.60	$99.60
Purchase #5	$47.29	7.177%	$50.684	$50.68	$50.70	$50.70
Purchase #6	$42.94	6.692%	$45.8135	$45.81	$45.80	$45.80
Purchase #7	$47.42	5.809%	$50.1746	$50.17	$50.15	$50.20
7 purchase totals =	$582.16		$620.9957	$620.99	$621.00	$621.00