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	$99.84	11.773%	$111.5942	$111.59	$111.60	$111.60
Purchase #2	$167.89	6.295%	$178.4587	$178.46	$178.45	$178.50
Purchase #3	$109.84	3.846%	$114.0644	$114.06	$114.05	$114.10
Purchase #4	$18.81	3.387%	$19.4471	$19.45	$19.45	$19.40
Purchase #5	$157.33	7.242%	$168.7238	$168.72	$168.70	$168.70
Purchase #6	$248.69	12.440%	$279.627	$279.63	$279.65	$279.60
Purchase #7	$113.36	12.183%	$127.1706	$127.17	$127.15	$127.20
7 purchase totals =	$915.76		$999.0858	$999.08	$999.05	$999.10