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	$16.79	4.608%	$17.5637	$17.56	$17.55	$17.60
Purchase #2	$233.47	6.788%	$249.3179	$249.32	$249.30	$249.30
Purchase #3	$132.50	10.570%	$146.5053	$146.51	$146.50	$146.50
Purchase #4	$68.52	13.853%	$78.0121	$78.01	$78.00	$78.00
Purchase #5	$37.98	11.636%	$42.3994	$42.40	$42.40	$42.40
Purchase #6	$93.35	8.523%	$101.3062	$101.31	$101.30	$101.30
Purchase #7	$250.92	9.528%	$274.8277	$274.83	$274.85	$274.80
7 purchase totals =	$833.53		$909.9323	$909.94	$909.90	$909.90