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	$17.99	11.854%	$20.1225	$20.12	$20.10	$20.10
Purchase #2	$233.35	3.782%	$242.1753	$242.18	$242.20	$242.20
Purchase #3	$33.82	9.615%	$37.0718	$37.07	$37.05	$37.10
Purchase #4	$42.85	7.870%	$46.2223	$46.22	$46.20	$46.20
Purchase #5	$33.68	10.366%	$37.1713	$37.17	$37.15	$37.20
Purchase #6	$55.25	10.724%	$61.175	$61.18	$61.20	$61.20
Purchase #7	$161.67	4.300%	$168.6218	$168.62	$168.60	$168.60
7 purchase totals =	$578.61		$612.5600	$612.56	$612.50	$612.60