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	$164.88	13.785%	$187.6087	$187.61	$187.60	$187.60
Purchase #2	$151.80	10.224%	$167.32	$167.32	$167.30	$167.30
Purchase #3	$17.41	8.239%	$18.8444	$18.84	$18.85	$18.80
Purchase #4	$53.73	10.278%	$59.2524	$59.25	$59.25	$59.30
Purchase #5	$161.51	11.769%	$180.5181	$180.52	$180.50	$180.50
Purchase #6	$38.26	6.857%	$40.8835	$40.88	$40.90	$40.90
Purchase #7	$25.99	9.434%	$28.4419	$28.44	$28.45	$28.40
7 purchase totals =	$613.58		$682.8690	$682.86	$682.85	$682.80