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	$86.70	4.272%	$90.4038	$90.40	$90.40	$90.40
Purchase #2	$16.78	10.831%	$18.5974	$18.60	$18.60	$18.60
Purchase #3	$250.66	5.266%	$263.8598	$263.86	$263.85	$263.90
Purchase #4	$29.65	13.361%	$33.6115	$33.61	$33.60	$33.60
Purchase #5	$15.62	9.476%	$17.1002	$17.10	$17.10	$17.10
Purchase #6	$67.66	10.628%	$74.8509	$74.85	$74.85	$74.90
Purchase #7	$29.57	11.782%	$33.0539	$33.05	$33.05	$33.10
7 purchase totals =	$496.64		$531.4775	$531.47	$531.45	$531.60