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	$102.60	3.694%	$106.39	$106.39	$106.40	$106.40
Purchase #2	$240.87	13.446%	$273.2574	$273.26	$273.25	$273.30
Purchase #3	$214.58	12.738%	$241.9132	$241.91	$241.90	$241.90
Purchase #4	$80.59	12.630%	$90.7685	$90.77	$90.75	$90.80
Purchase #5	$19.50	5.590%	$20.5901	$20.59	$20.60	$20.60
Purchase #6	$21.35	6.116%	$22.6558	$22.66	$22.65	$22.70
Purchase #7	$82.36	12.327%	$92.5125	$92.51	$92.50	$92.50
7 purchase totals =	$761.85		$848.0875	$848.09	$848.05	$848.20