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	$159.59	6.337%	$169.7032	$169.70	$169.70	$169.70
Purchase #2	$71.47	10.760%	$79.1602	$79.16	$79.15	$79.20
Purchase #3	$131.59	4.564%	$137.5958	$137.60	$137.60	$137.60
Purchase #4	$222.68	8.200%	$240.9398	$240.94	$240.95	$240.90
Purchase #5	$176.51	11.453%	$196.7257	$196.73	$196.75	$196.70
Purchase #6	$41.73	10.820%	$46.2452	$46.25	$46.25	$46.20
Purchase #7	$58.37	13.856%	$66.4577	$66.46	$66.45	$66.50
7 purchase totals =	$861.94		$936.8276	$936.84	$936.85	$936.80