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	$85.44	4.671%	$89.4309	$89.43	$89.45	$89.40
Purchase #2	$158.86	8.625%	$172.5617	$172.56	$172.55	$172.60
Purchase #3	$179.48	10.655%	$198.6036	$198.60	$198.60	$198.60
Purchase #4	$96.65	13.782%	$109.9703	$109.97	$109.95	$110.00
Purchase #5	$24.92	6.271%	$26.4827	$26.48	$26.50	$26.50
Purchase #6	$237.72	9.611%	$260.5673	$260.57	$260.55	$260.60
Purchase #7	$52.68	12.418%	$59.2218	$59.22	$59.20	$59.20
7 purchase totals =	$835.75		$916.8383	$916.83	$916.80	$916.90