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	$233.55	11.265%	$259.8594	$259.86	$259.85	$259.90
Purchase #2	$171.82	7.844%	$185.2976	$185.30	$185.30	$185.30
Purchase #3	$234.63	13.402%	$266.0751	$266.08	$266.10	$266.10
Purchase #4	$127.74	13.267%	$144.6873	$144.69	$144.70	$144.70
Purchase #5	$51.58	5.704%	$54.5221	$54.52	$54.50	$54.50
Purchase #6	$32.53	7.333%	$34.9154	$34.92	$34.90	$34.90
Purchase #7	$163.79	5.511%	$172.8165	$172.82	$172.80	$172.80
7 purchase totals =	$1,015.64		$1,118.1734	$1,118.19	$1,118.15	$1,118.20