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	$124.30	13.516%	$141.1004	$141.10	$141.10	$141.10
Purchase #2	$101.66	11.464%	$113.3143	$113.31	$113.30	$113.30
Purchase #3	$32.93	5.103%	$34.6104	$34.61	$34.60	$34.60
Purchase #4	$109.83	4.443%	$114.7097	$114.71	$114.70	$114.70
Purchase #5	$191.29	4.702%	$200.2845	$200.28	$200.30	$200.30
Purchase #6	$200.25	3.364%	$206.9864	$206.99	$207.00	$207.00
Purchase #7	$78.28	10.434%	$86.4477	$86.45	$86.45	$86.40
7 purchase totals =	$838.54		$897.4534	$897.45	$897.45	$897.40