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	$77.66	9.336%	$84.9103	$84.91	$84.90	$84.90
Purchase #2	$137.31	13.246%	$155.4981	$155.50	$155.50	$155.50
Purchase #3	$39.40	4.772%	$41.2802	$41.28	$41.30	$41.30
Purchase #4	$128.54	7.629%	$138.3463	$138.35	$138.35	$138.30
Purchase #5	$35.96	4.548%	$37.5955	$37.60	$37.60	$37.60
Purchase #6	$250.42	11.167%	$278.3844	$278.38	$278.40	$278.40
Purchase #7	$32.72	13.855%	$37.2534	$37.25	$37.25	$37.30
7 purchase totals =	$702.01		$773.2682	$773.27	$773.30	$773.30