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	$42.75	6.414%	$45.492	$45.49	$45.50	$45.50
Purchase #2	$91.83	12.800%	$103.5842	$103.58	$103.60	$103.60
Purchase #3	$53.49	6.318%	$56.8695	$56.87	$56.85	$56.90
Purchase #4	$152.44	8.544%	$165.4645	$165.46	$165.45	$165.50
Purchase #5	$204.82	4.243%	$213.5105	$213.51	$213.50	$213.50
Purchase #6	$32.68	4.506%	$34.1526	$34.15	$34.15	$34.20
Purchase #7	$92.95	6.253%	$98.7622	$98.76	$98.75	$98.80
7 purchase totals =	$670.96		$717.8355	$717.82	$717.80	$718.00