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	$53.25	5.162%	$55.9988	$56.00	$56.00	$56.00
Purchase #2	$59.38	9.329%	$64.9196	$64.92	$64.90	$64.90
Purchase #3	$83.68	7.750%	$90.1652	$90.17	$90.15	$90.20
Purchase #4	$95.84	4.853%	$100.4911	$100.49	$100.50	$100.50
Purchase #5	$116.39	10.507%	$128.6191	$128.62	$128.60	$128.60
Purchase #6	$140.68	5.315%	$148.1571	$148.16	$148.15	$148.20
Purchase #7	$22.54	6.658%	$24.0407	$24.04	$24.05	$24.00
7 purchase totals =	$571.76		$612.3916	$612.40	$612.35	$612.40