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	$25.85	13.663%	$29.3819	$29.38	$29.40	$29.40
Purchase #2	$59.89	10.317%	$66.0689	$66.07	$66.05	$66.10
Purchase #3	$238.87	10.750%	$264.5485	$264.55	$264.55	$264.50
Purchase #4	$91.83	4.621%	$96.0735	$96.07	$96.05	$96.10
Purchase #5	$117.98	7.226%	$126.5052	$126.51	$126.50	$126.50
Purchase #6	$86.47	12.282%	$97.0902	$97.09	$97.10	$97.10
Purchase #7	$18.66	10.278%	$20.5779	$20.58	$20.60	$20.60
7 purchase totals =	$639.55		$700.2461	$700.25	$700.25	$700.30