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	$21.31	8.834%	$23.1925	$23.19	$23.20	$23.20
Purchase #2	$157.32	9.268%	$171.9004	$171.90	$171.90	$171.90
Purchase #3	$148.37	13.641%	$168.6092	$168.61	$168.60	$168.60
Purchase #4	$150.89	5.792%	$159.6295	$159.63	$159.65	$159.60
Purchase #5	$92.63	13.874%	$105.4815	$105.48	$105.50	$105.50
Purchase #6	$6.74	10.112%	$7.4215	$7.42	$7.40	$7.40
Purchase #7	$90.77	12.577%	$102.1861	$102.19	$102.20	$102.20
7 purchase totals =	$668.03		$738.4207	$738.42	$738.45	$738.40