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	$81.50	11.459%	$90.8391	$90.84	$90.85	$90.80
Purchase #2	$121.61	10.671%	$134.587	$134.59	$134.60	$134.60
Purchase #3	$224.85	6.804%	$240.1488	$240.15	$240.15	$240.10
Purchase #4	$142.62	8.246%	$154.3804	$154.38	$154.40	$154.40
Purchase #5	$9.66	3.578%	$10.0056	$10.01	$10.00	$10.00
Purchase #6	$74.50	3.678%	$77.2401	$77.24	$77.25	$77.20
Purchase #7	$118.83	10.704%	$131.5496	$131.55	$131.55	$131.50
7 purchase totals =	$773.57		$838.7506	$838.76	$838.80	$838.60