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	$151.57	3.698%	$157.1751	$157.18	$157.20	$157.20
Purchase #2	$41.47	8.551%	$45.0161	$45.02	$45.00	$45.00
Purchase #3	$34.73	9.599%	$38.0637	$38.06	$38.05	$38.10
Purchase #4	$169.78	4.866%	$178.0415	$178.04	$178.05	$178.00
Purchase #5	$119.70	6.794%	$127.8324	$127.83	$127.85	$127.80
Purchase #6	$23.39	12.465%	$26.3056	$26.31	$26.30	$26.30
Purchase #7	$20.32	4.184%	$21.1702	$21.17	$21.15	$21.20
7 purchase totals =	$560.96		$593.6046	$593.61	$593.60	$593.60