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	$37.64	6.726%	$40.1717	$40.17	$40.15	$40.20
Purchase #2	$87.69	3.111%	$90.418	$90.42	$90.40	$90.40
Purchase #3	$140.53	7.866%	$151.5841	$151.58	$151.60	$151.60
Purchase #4	$188.47	10.817%	$208.8568	$208.86	$208.85	$208.90
Purchase #5	$160.98	6.537%	$171.5033	$171.50	$171.50	$171.50
Purchase #6	$140.92	12.129%	$158.0122	$158.01	$158.00	$158.00
Purchase #7	$140.38	7.759%	$151.2721	$151.27	$151.25	$151.30
7 purchase totals =	$896.61		$971.8182	$971.81	$971.75	$971.90