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	$10.43	7.818%	$11.2454	$11.25	$11.25	$11.20
Purchase #2	$110.51	8.177%	$119.5464	$119.55	$119.55	$119.50
Purchase #3	$173.99	5.123%	$182.9035	$182.90	$182.90	$182.90
Purchase #4	$239.82	6.397%	$255.1613	$255.16	$255.15	$255.20
Purchase #5	$222.77	9.526%	$243.9911	$243.99	$244.00	$244.00
Purchase #6	$128.59	13.171%	$145.5266	$145.53	$145.55	$145.50
Purchase #7	$118.87	10.702%	$131.5915	$131.59	$131.60	$131.60
7 purchase totals =	$1,004.98		$1,089.9658	$1,089.97	$1,090.00	$1,089.90