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	$212.35	4.836%	$222.6192	$222.62	$222.60	$222.60
Purchase #2	$232.32	12.278%	$260.8442	$260.84	$260.85	$260.80
Purchase #3	$31.57	11.395%	$35.1674	$35.17	$35.15	$35.20
Purchase #4	$115.79	13.600%	$131.5374	$131.54	$131.55	$131.50
Purchase #5	$58.87	13.264%	$66.6785	$66.68	$66.70	$66.70
Purchase #6	$28.43	13.429%	$32.2479	$32.25	$32.25	$32.20
Purchase #7	$38.33	8.386%	$41.5444	$41.54	$41.55	$41.50
7 purchase totals =	$717.66		$790.6390	$790.64	$790.65	$790.50