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	$146.50	12.643%	$165.022	$165.02	$165.00	$165.00
Purchase #2	$230.51	9.522%	$252.4592	$252.46	$252.45	$252.50
Purchase #3	$201.99	11.554%	$225.3279	$225.33	$225.35	$225.30
Purchase #4	$218.89	13.677%	$248.8276	$248.83	$248.85	$248.80
Purchase #5	$85.97	4.503%	$89.8412	$89.84	$89.85	$89.80
Purchase #6	$51.96	7.445%	$55.8284	$55.83	$55.85	$55.80
Purchase #7	$67.30	11.663%	$75.1492	$75.15	$75.15	$75.10
7 purchase totals =	$1,003.12		$1,112.4555	$1,112.46	$1,112.50	$1,112.30