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	$132.89	10.536%	$146.8913	$146.89	$146.90	$146.90
Purchase #2	$59.31	12.145%	$66.5132	$66.51	$66.50	$66.50
Purchase #3	$204.68	5.224%	$215.3725	$215.37	$215.35	$215.40
Purchase #4	$81.83	5.566%	$86.3847	$86.38	$86.40	$86.40
Purchase #5	$82.87	7.823%	$89.3529	$89.35	$89.35	$89.40
Purchase #6	$207.59	3.727%	$215.3269	$215.33	$215.35	$215.30
Purchase #7	$142.80	6.437%	$151.992	$151.99	$152.00	$152.00
7 purchase totals =	$911.97		$971.8335	$971.82	$971.85	$971.90