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	$80.32	13.187%	$90.9118	$90.91	$90.90	$90.90
Purchase #2	$127.47	4.205%	$132.8301	$132.83	$132.85	$132.80
Purchase #3	$34.36	9.776%	$37.719	$37.72	$37.70	$37.70
Purchase #4	$87.42	12.773%	$98.5862	$98.59	$98.60	$98.60
Purchase #5	$106.29	5.794%	$112.4484	$112.45	$112.45	$112.40
Purchase #6	$178.63	4.283%	$186.2807	$186.28	$186.30	$186.30
Purchase #7	$129.72	7.107%	$138.9392	$138.94	$138.95	$138.90
7 purchase totals =	$744.21		$797.7154	$797.72	$797.75	$797.60