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	$34.41	10.178%	$37.9122	$37.91	$37.90	$37.90
Purchase #2	$131.36	12.463%	$147.7314	$147.73	$147.75	$147.70
Purchase #3	$119.83	9.668%	$131.4152	$131.42	$131.40	$131.40
Purchase #4	$44.50	3.236%	$45.94	$45.94	$45.95	$45.90
Purchase #5	$11.48	7.639%	$12.357	$12.36	$12.35	$12.40
Purchase #6	$203.71	5.262%	$214.4292	$214.43	$214.45	$214.40
Purchase #7	$44.58	8.759%	$48.4848	$48.48	$48.50	$48.50
7 purchase totals =	$589.87		$638.2698	$638.27	$638.30	$638.20