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	$184.84	13.618%	$210.0115	$210.01	$210.00	$210.00
Purchase #2	$34.83	7.553%	$37.4607	$37.46	$37.45	$37.50
Purchase #3	$80.30	11.166%	$89.2663	$89.27	$89.25	$89.30
Purchase #4	$16.54	9.436%	$18.1007	$18.10	$18.10	$18.10
Purchase #5	$8.58	4.870%	$8.9978	$9.00	$9.00	$9.00
Purchase #6	$118.33	3.212%	$122.1308	$122.13	$122.15	$122.10
Purchase #7	$234.87	8.772%	$255.4728	$255.47	$255.45	$255.50
7 purchase totals =	$678.29		$741.4406	$741.44	$741.40	$741.50