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	$25.44	13.274%	$28.8169	$28.82	$28.80	$28.80
Purchase #2	$230.88	10.476%	$255.067	$255.07	$255.05	$255.10
Purchase #3	$49.30	13.497%	$55.954	$55.95	$55.95	$56.00
Purchase #4	$57.55	13.822%	$65.5046	$65.50	$65.50	$65.50
Purchase #5	$130.80	4.603%	$136.8207	$136.82	$136.80	$136.80
Purchase #6	$66.72	5.849%	$70.6225	$70.62	$70.60	$70.60
Purchase #7	$50.51	6.869%	$53.9795	$53.98	$54.00	$54.00
7 purchase totals =	$611.20		$666.7652	$666.76	$666.70	$666.80