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	$139.37	7.685%	$150.0806	$150.08	$150.10	$150.10
Purchase #2	$47.97	13.182%	$54.2934	$54.29	$54.30	$54.30
Purchase #3	$56.50	11.583%	$63.0444	$63.04	$63.05	$63.00
Purchase #4	$67.92	5.696%	$71.7887	$71.79	$71.80	$71.80
Purchase #5	$196.47	6.469%	$209.1796	$209.18	$209.20	$209.20
Purchase #6	$87.75	13.521%	$99.6147	$99.61	$99.60	$99.60
Purchase #7	$21.79	9.838%	$23.9337	$23.93	$23.95	$23.90
7 purchase totals =	$617.77		$671.9351	$671.92	$672.00	$671.90