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	$107.35	10.363%	$118.4747	$118.47	$118.45	$118.50
Purchase #2	$47.89	5.517%	$50.5321	$50.53	$50.55	$50.50
Purchase #3	$137.95	5.293%	$145.2517	$145.25	$145.25	$145.30
Purchase #4	$79.83	12.429%	$89.7521	$89.75	$89.75	$89.80
Purchase #5	$27.67	7.608%	$29.7751	$29.78	$29.80	$29.80
Purchase #6	$242.32	6.520%	$258.1193	$258.12	$258.10	$258.10
Purchase #7	$73.77	6.441%	$78.5215	$78.52	$78.50	$78.50
7 purchase totals =	$716.78		$770.4265	$770.42	$770.40	$770.50