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	$91.60	12.615%	$103.1553	$103.16	$103.15	$103.20
Purchase #2	$142.73	3.583%	$147.844	$147.84	$147.85	$147.80
Purchase #3	$242.75	5.411%	$255.8852	$255.89	$255.90	$255.90
Purchase #4	$38.30	5.590%	$40.441	$40.44	$40.45	$40.40
Purchase #5	$78.98	9.623%	$86.5802	$86.58	$86.60	$86.60
Purchase #6	$18.86	3.458%	$19.5122	$19.51	$19.50	$19.50
Purchase #7	$34.81	5.204%	$36.6215	$36.62	$36.60	$36.60
7 purchase totals =	$648.03		$690.0394	$690.04	$690.05	$690.00