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	$43.58	5.294%	$45.8871	$45.89	$45.90	$45.90
Purchase #2	$100.65	11.721%	$112.4472	$112.45	$112.45	$112.40
Purchase #3	$73.96	5.126%	$77.7512	$77.75	$77.75	$77.80
Purchase #4	$127.85	5.200%	$134.4982	$134.50	$134.50	$134.50
Purchase #5	$28.95	6.124%	$30.7229	$30.72	$30.70	$30.70
Purchase #6	$155.45	12.739%	$175.2528	$175.25	$175.25	$175.30
Purchase #7	$227.70	12.173%	$255.4179	$255.42	$255.40	$255.40
7 purchase totals =	$758.14		$831.9773	$831.98	$831.95	$832.00