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	$230.75	6.491%	$245.728	$245.73	$245.75	$245.70
Purchase #2	$216.81	12.805%	$244.5725	$244.57	$244.55	$244.60
Purchase #3	$176.27	7.102%	$188.7887	$188.79	$188.80	$188.80
Purchase #4	$95.74	7.685%	$103.0976	$103.10	$103.10	$103.10
Purchase #5	$78.81	12.713%	$88.8291	$88.83	$88.85	$88.80
Purchase #6	$175.35	7.815%	$189.0536	$189.05	$189.05	$189.10
Purchase #7	$26.56	12.269%	$29.8186	$29.82	$29.80	$29.80
7 purchase totals =	$1,000.29		$1,089.8881	$1,089.89	$1,089.90	$1,089.90