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	$41.86	4.434%	$43.7161	$43.72	$43.70	$43.70
Purchase #2	$106.73	4.632%	$111.6737	$111.67	$111.65	$111.70
Purchase #3	$16.35	8.352%	$17.7156	$17.72	$17.70	$17.70
Purchase #4	$132.50	4.604%	$138.6003	$138.60	$138.60	$138.60
Purchase #5	$150.60	9.559%	$164.9959	$165.00	$165.00	$165.00
Purchase #6	$27.71	9.446%	$30.3275	$30.33	$30.35	$30.30
Purchase #7	$84.29	7.640%	$90.7298	$90.73	$90.75	$90.70
7 purchase totals =	$560.04		$597.7589	$597.77	$597.75	$597.70