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	$8.44	4.165%	$8.7915	$8.79	$8.80	$8.80
Purchase #2	$86.79	3.222%	$89.5864	$89.59	$89.60	$89.60
Purchase #3	$165.68	9.529%	$181.4676	$181.47	$181.45	$181.50
Purchase #4	$60.35	5.373%	$63.5926	$63.59	$63.60	$63.60
Purchase #5	$150.95	9.557%	$165.3763	$165.38	$165.40	$165.40
Purchase #6	$105.77	11.704%	$118.1493	$118.15	$118.15	$118.10
Purchase #7	$222.80	8.458%	$241.6444	$241.64	$241.65	$241.60
7 purchase totals =	$800.78		$868.6081	$868.61	$868.65	$868.60