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	$39.77	6.809%	$42.4779	$42.48	$42.50	$42.50
Purchase #2	$214.92	5.334%	$226.3838	$226.38	$226.40	$226.40
Purchase #3	$176.47	11.326%	$196.457	$196.46	$196.45	$196.50
Purchase #4	$26.57	10.806%	$29.4412	$29.44	$29.45	$29.40
Purchase #5	$183.85	11.606%	$205.1876	$205.19	$205.20	$205.20
Purchase #6	$72.62	6.324%	$77.2125	$77.21	$77.20	$77.20
Purchase #7	$215.61	3.130%	$222.3586	$222.36	$222.35	$222.40
7 purchase totals =	$929.81		$999.5186	$999.52	$999.55	$999.60