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	$229.25	8.170%	$247.9797	$247.98	$248.00	$248.00
Purchase #2	$42.30	7.581%	$45.5068	$45.51	$45.50	$45.50
Purchase #3	$230.83	4.787%	$241.8798	$241.88	$241.90	$241.90
Purchase #4	$49.89	6.130%	$52.9483	$52.95	$52.95	$52.90
Purchase #5	$57.40	8.593%	$62.3324	$62.33	$62.35	$62.30
Purchase #6	$132.54	3.179%	$136.7534	$136.75	$136.75	$136.80
Purchase #7	$44.60	8.638%	$48.4525	$48.45	$48.45	$48.50
7 purchase totals =	$786.81		$835.8529	$835.85	$835.90	$835.90