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	$246.68	3.400%	$255.0671	$255.07	$255.05	$255.10
Purchase #2	$74.99	6.868%	$80.1403	$80.14	$80.15	$80.10
Purchase #3	$111.47	12.761%	$125.6947	$125.69	$125.70	$125.70
Purchase #4	$112.81	9.770%	$123.8315	$123.83	$123.85	$123.80
Purchase #5	$96.25	13.294%	$109.0455	$109.05	$109.05	$109.00
Purchase #6	$101.68	7.769%	$109.5795	$109.58	$109.60	$109.60
Purchase #7	$57.61	6.586%	$61.4042	$61.40	$61.40	$61.40
7 purchase totals =	$801.49		$864.7628	$864.76	$864.80	$864.70