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	$12.60	4.287%	$13.1402	$13.14	$13.15	$13.10
Purchase #2	$81.55	10.188%	$89.8583	$89.86	$89.85	$89.90
Purchase #3	$33.81	3.784%	$35.0894	$35.09	$35.10	$35.10
Purchase #4	$61.91	10.191%	$68.2192	$68.22	$68.20	$68.20
Purchase #5	$130.61	10.591%	$144.4429	$144.44	$144.45	$144.40
Purchase #6	$74.90	11.305%	$83.3674	$83.37	$83.35	$83.40
Purchase #7	$118.64	12.781%	$133.8034	$133.80	$133.80	$133.80
7 purchase totals =	$514.02		$567.9208	$567.92	$567.90	$567.90