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	$18.95	13.735%	$21.5528	$21.55	$21.55	$21.60
Purchase #2	$153.97	6.692%	$164.2737	$164.27	$164.25	$164.30
Purchase #3	$79.74	4.852%	$83.609	$83.61	$83.60	$83.60
Purchase #4	$19.60	3.865%	$20.3575	$20.36	$20.35	$20.40
Purchase #5	$45.58	11.673%	$50.9006	$50.90	$50.90	$50.90
Purchase #6	$221.33	11.205%	$246.13	$246.13	$246.15	$246.10
Purchase #7	$158.46	8.561%	$172.0258	$172.03	$172.05	$172.00
7 purchase totals =	$697.63		$758.8494	$758.85	$758.85	$758.90