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	$153.51	8.341%	$166.3143	$166.31	$166.30	$166.30
Purchase #2	$70.89	8.468%	$76.893	$76.89	$76.90	$76.90
Purchase #3	$131.75	11.423%	$146.7998	$146.80	$146.80	$146.80
Purchase #4	$232.85	9.649%	$255.3177	$255.32	$255.30	$255.30
Purchase #5	$132.35	9.254%	$144.5977	$144.60	$144.60	$144.60
Purchase #6	$37.25	7.472%	$40.0333	$40.03	$40.05	$40.00
Purchase #7	$72.96	7.282%	$78.2729	$78.27	$78.25	$78.30
7 purchase totals =	$831.56		$908.2287	$908.22	$908.20	$908.20