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	$126.87	13.789%	$144.3641	$144.36	$144.35	$144.40
Purchase #2	$241.49	3.865%	$250.8236	$250.82	$250.80	$250.80
Purchase #3	$59.41	12.363%	$66.7549	$66.75	$66.75	$66.80
Purchase #4	$149.77	4.506%	$156.5186	$156.52	$156.50	$156.50
Purchase #5	$221.39	8.309%	$239.7853	$239.79	$239.80	$239.80
Purchase #6	$7.51	13.381%	$8.5149	$8.51	$8.50	$8.50
Purchase #7	$118.38	4.602%	$123.8278	$123.83	$123.85	$123.80
7 purchase totals =	$924.82		$990.5892	$990.58	$990.55	$990.60