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	$70.79	13.136%	$80.089	$80.09	$80.10	$80.10
Purchase #2	$182.81	7.545%	$196.603	$196.60	$196.60	$196.60
Purchase #3	$94.95	12.666%	$106.9764	$106.98	$107.00	$107.00
Purchase #4	$158.71	9.269%	$173.4208	$173.42	$173.40	$173.40
Purchase #5	$26.30	7.211%	$28.1965	$28.20	$28.20	$28.20
Purchase #6	$86.50	4.537%	$90.4245	$90.42	$90.40	$90.40
Purchase #7	$239.56	3.738%	$248.5148	$248.51	$248.50	$248.50
7 purchase totals =	$859.62		$924.2250	$924.22	$924.20	$924.20