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	$128.59	6.291%	$136.6796	$136.68	$136.70	$136.70
Purchase #2	$25.83	5.169%	$27.1652	$27.17	$27.15	$27.20
Purchase #3	$81.81	10.614%	$90.4933	$90.49	$90.50	$90.50
Purchase #4	$165.89	8.745%	$180.3971	$180.40	$180.40	$180.40
Purchase #5	$45.51	11.531%	$50.7578	$50.76	$50.75	$50.80
Purchase #6	$199.90	4.192%	$208.2798	$208.28	$208.30	$208.30
Purchase #7	$191.39	13.856%	$217.909	$217.91	$217.90	$217.90
7 purchase totals =	$838.92		$911.6818	$911.69	$911.70	$911.80