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	$16.35	10.309%	$18.0355	$18.04	$18.05	$18.00
Purchase #2	$114.61	11.172%	$127.4142	$127.41	$127.40	$127.40
Purchase #3	$107.38	10.161%	$118.2909	$118.29	$118.30	$118.30
Purchase #4	$126.89	13.529%	$144.0569	$144.06	$144.05	$144.10
Purchase #5	$41.25	3.358%	$42.6352	$42.64	$42.65	$42.60
Purchase #6	$187.29	12.259%	$210.2499	$210.25	$210.25	$210.20
Purchase #7	$117.67	9.152%	$128.4392	$128.44	$128.45	$128.40
7 purchase totals =	$711.44		$789.1218	$789.13	$789.15	$789.00