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	$158.67	12.825%	$179.0194	$179.02	$179.00	$179.00
Purchase #2	$113.30	12.763%	$127.7605	$127.76	$127.75	$127.80
Purchase #3	$36.74	8.808%	$39.9761	$39.98	$40.00	$40.00
Purchase #4	$214.78	5.839%	$227.321	$227.32	$227.30	$227.30
Purchase #5	$62.59	12.183%	$70.2153	$70.22	$70.20	$70.20
Purchase #6	$117.39	13.172%	$132.8526	$132.85	$132.85	$132.90
Purchase #7	$22.90	5.757%	$24.2184	$24.22	$24.20	$24.20
7 purchase totals =	$726.37		$801.3633	$801.37	$801.30	$801.40