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	$127.62	9.136%	$139.2794	$139.28	$139.30	$139.30
Purchase #2	$53.37	4.725%	$55.8917	$55.89	$55.90	$55.90
Purchase #3	$146.79	4.835%	$153.8873	$153.89	$153.90	$153.90
Purchase #4	$127.41	3.182%	$131.4642	$131.46	$131.45	$131.50
Purchase #5	$217.60	8.187%	$235.4149	$235.41	$235.40	$235.40
Purchase #6	$89.79	8.642%	$97.5497	$97.55	$97.55	$97.50
Purchase #7	$100.73	6.564%	$107.3419	$107.34	$107.35	$107.30
7 purchase totals =	$863.31		$920.8291	$920.82	$920.85	$920.80