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	$128.88	12.863%	$145.4578	$145.46	$145.45	$145.50
Purchase #2	$60.54	8.379%	$65.6126	$65.61	$65.60	$65.60
Purchase #3	$122.91	4.586%	$128.5467	$128.55	$128.55	$128.50
Purchase #4	$156.61	13.303%	$177.4438	$177.44	$177.45	$177.40
Purchase #5	$200.98	12.595%	$226.2934	$226.29	$226.30	$226.30
Purchase #6	$100.44	10.811%	$111.2986	$111.30	$111.30	$111.30
Purchase #7	$29.86	11.862%	$33.402	$33.40	$33.40	$33.40
7 purchase totals =	$800.22		$888.0549	$888.05	$888.05	$888.00