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	$52.95	3.860%	$54.9939	$54.99	$55.00	$55.00
Purchase #2	$55.96	5.465%	$59.0182	$59.02	$59.00	$59.00
Purchase #3	$133.31	13.429%	$151.2122	$151.21	$151.20	$151.20
Purchase #4	$49.72	12.771%	$56.0697	$56.07	$56.05	$56.10
Purchase #5	$130.66	10.151%	$143.9233	$143.92	$143.90	$143.90
Purchase #6	$94.77	8.604%	$102.924	$102.92	$102.90	$102.90
Purchase #7	$92.50	9.613%	$101.392	$101.39	$101.40	$101.40
7 purchase totals =	$609.87		$669.5333	$669.52	$669.45	$669.50