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	$16.73	11.273%	$18.616	$18.62	$18.60	$18.60
Purchase #2	$211.71	11.126%	$235.2649	$235.26	$235.25	$235.30
Purchase #3	$80.28	12.428%	$90.2572	$90.26	$90.25	$90.30
Purchase #4	$123.36	7.171%	$132.2061	$132.21	$132.20	$132.20
Purchase #5	$56.54	8.769%	$61.498	$61.50	$61.50	$61.50
Purchase #6	$167.76	11.526%	$187.096	$187.10	$187.10	$187.10
Purchase #7	$28.39	10.204%	$31.2869	$31.29	$31.30	$31.30
7 purchase totals =	$684.77		$756.2251	$756.24	$756.20	$756.30