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	$72.78	7.858%	$78.4991	$78.50	$78.50	$78.50
Purchase #2	$153.47	11.443%	$171.0316	$171.03	$171.05	$171.00
Purchase #3	$222.95	13.255%	$252.502	$252.50	$252.50	$252.50
Purchase #4	$114.73	6.472%	$122.1553	$122.16	$122.15	$122.20
Purchase #5	$134.44	10.187%	$148.1354	$148.14	$148.15	$148.10
Purchase #6	$80.52	7.390%	$86.4704	$86.47	$86.45	$86.50
Purchase #7	$113.94	4.718%	$119.3157	$119.32	$119.30	$119.30
7 purchase totals =	$892.83		$978.1095	$978.12	$978.10	$978.10