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	$211.43	7.585%	$227.467	$227.47	$227.45	$227.50
Purchase #2	$133.34	9.258%	$145.6846	$145.68	$145.70	$145.70
Purchase #3	$88.78	13.155%	$100.459	$100.46	$100.45	$100.50
Purchase #4	$15.60	12.822%	$17.6002	$17.60	$17.60	$17.60
Purchase #5	$42.55	13.537%	$48.31	$48.31	$48.30	$48.30
Purchase #6	$29.96	9.502%	$32.8068	$32.81	$32.80	$32.80
Purchase #7	$7.66	10.190%	$8.4406	$8.44	$8.45	$8.40
7 purchase totals =	$529.32		$580.7682	$580.77	$580.75	$580.80