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	$14.43	5.600%	$15.2381	$15.24	$15.25	$15.20
Purchase #2	$206.73	11.543%	$230.5928	$230.59	$230.60	$230.60
Purchase #3	$12.69	12.635%	$14.2934	$14.29	$14.30	$14.30
Purchase #4	$34.47	9.738%	$37.8267	$37.83	$37.85	$37.80
Purchase #5	$78.50	13.235%	$88.8895	$88.89	$88.90	$88.90
Purchase #6	$84.97	8.442%	$92.1432	$92.14	$92.15	$92.10
Purchase #7	$26.82	3.754%	$27.8268	$27.83	$27.85	$27.80
7 purchase totals =	$458.61		$506.8105	$506.81	$506.90	$506.70