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	$28.35	11.759%	$31.6837	$31.68	$31.70	$31.70
Purchase #2	$38.64	5.542%	$40.7814	$40.78	$40.80	$40.80
Purchase #3	$93.38	7.690%	$100.5609	$100.56	$100.55	$100.60
Purchase #4	$134.48	12.451%	$151.2241	$151.22	$151.20	$151.20
Purchase #5	$178.97	4.696%	$187.3744	$187.37	$187.35	$187.40
Purchase #6	$126.50	8.472%	$137.2171	$137.22	$137.20	$137.20
Purchase #7	$169.61	9.290%	$185.3668	$185.37	$185.35	$185.40
7 purchase totals =	$769.93		$834.2084	$834.20	$834.15	$834.30