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	$31.26	13.162%	$35.3744	$35.37	$35.35	$35.40
Purchase #2	$84.68	5.287%	$89.157	$89.16	$89.15	$89.20
Purchase #3	$53.72	12.403%	$60.3829	$60.38	$60.40	$60.40
Purchase #4	$204.77	9.866%	$224.9726	$224.97	$224.95	$225.00
Purchase #5	$166.51	9.772%	$182.7814	$182.78	$182.80	$182.80
Purchase #6	$100.51	8.471%	$109.0242	$109.02	$109.00	$109.00
Purchase #7	$169.83	10.601%	$187.8337	$187.83	$187.85	$187.80
7 purchase totals =	$811.28		$889.5262	$889.51	$889.50	$889.60