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	$132.60	5.496%	$139.8877	$139.89	$139.90	$139.90
Purchase #2	$124.62	9.195%	$136.0788	$136.08	$136.10	$136.10
Purchase #3	$91.72	11.635%	$102.3916	$102.39	$102.40	$102.40
Purchase #4	$152.45	4.851%	$159.8453	$159.85	$159.85	$159.80
Purchase #5	$27.59	7.249%	$29.59	$29.59	$29.60	$29.60
Purchase #6	$175.87	7.717%	$189.4419	$189.44	$189.45	$189.40
Purchase #7	$135.77	11.483%	$151.3605	$151.36	$151.35	$151.40
7 purchase totals =	$840.62		$908.5958	$908.60	$908.65	$908.60