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	$51.73	11.582%	$57.7214	$57.72	$57.70	$57.70
Purchase #2	$228.47	13.599%	$259.5396	$259.54	$259.55	$259.50
Purchase #3	$86.50	9.255%	$94.5056	$94.51	$94.50	$94.50
Purchase #4	$53.82	9.738%	$59.061	$59.06	$59.05	$59.10
Purchase #5	$49.49	9.434%	$54.1589	$54.16	$54.15	$54.20
Purchase #6	$94.57	8.627%	$102.7286	$102.73	$102.75	$102.70
Purchase #7	$229.92	13.788%	$261.6214	$261.62	$261.60	$261.60
7 purchase totals =	$794.50		$889.3365	$889.34	$889.30	$889.30