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	$69.38	12.837%	$78.2863	$78.29	$78.30	$78.30
Purchase #2	$203.63	13.851%	$231.8348	$231.83	$231.85	$231.80
Purchase #3	$12.38	13.421%	$14.0415	$14.04	$14.05	$14.00
Purchase #4	$91.25	13.728%	$103.7768	$103.78	$103.80	$103.80
Purchase #5	$98.96	9.773%	$108.6314	$108.63	$108.65	$108.60
Purchase #6	$87.73	8.778%	$95.4309	$95.43	$95.45	$95.40
Purchase #7	$79.74	12.270%	$89.5241	$89.52	$89.50	$89.50
7 purchase totals =	$643.07		$721.5258	$721.52	$721.60	$721.40