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	$59.91	13.141%	$67.7828	$67.78	$67.80	$67.80
Purchase #2	$132.84	10.299%	$146.5212	$146.52	$146.50	$146.50
Purchase #3	$90.60	10.626%	$100.2272	$100.23	$100.25	$100.20
Purchase #4	$13.61	6.331%	$14.4716	$14.47	$14.45	$14.50
Purchase #5	$5.57	7.689%	$5.9983	$6.00	$6.00	$6.00
Purchase #6	$145.75	4.751%	$152.6746	$152.67	$152.65	$152.70
Purchase #7	$63.26	5.805%	$66.9322	$66.93	$66.95	$66.90
7 purchase totals =	$511.54		$554.6079	$554.60	$554.60	$554.60