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	$84.96	6.435%	$90.4272	$90.43	$90.45	$90.40
Purchase #2	$18.74	10.357%	$20.6809	$20.68	$20.70	$20.70
Purchase #3	$234.40	10.548%	$259.1245	$259.12	$259.10	$259.10
Purchase #4	$141.28	6.785%	$150.8658	$150.87	$150.85	$150.90
Purchase #5	$172.49	4.457%	$180.1779	$180.18	$180.20	$180.20
Purchase #6	$115.52	13.849%	$131.5184	$131.52	$131.50	$131.50
Purchase #7	$157.45	9.735%	$172.7778	$172.78	$172.80	$172.80
7 purchase totals =	$924.84		$1,005.5725	$1,005.58	$1,005.60	$1,005.60