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	$126.47	12.160%	$141.8488	$141.85	$141.85	$141.80
Purchase #2	$199.38	10.734%	$220.7814	$220.78	$220.80	$220.80
Purchase #3	$60.68	11.409%	$67.603	$67.60	$67.60	$67.60
Purchase #4	$86.90	13.370%	$98.5185	$98.52	$98.50	$98.50
Purchase #5	$134.90	6.353%	$143.4702	$143.47	$143.45	$143.50
Purchase #6	$92.91	12.837%	$104.8369	$104.84	$104.85	$104.80
Purchase #7	$26.74	9.333%	$29.2356	$29.24	$29.25	$29.20
7 purchase totals =	$727.98		$806.2944	$806.30	$806.30	$806.20