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	$66.65	6.365%	$70.8923	$70.89	$70.90	$70.90
Purchase #2	$77.33	11.309%	$86.0752	$86.08	$86.10	$86.10
Purchase #3	$148.78	10.239%	$164.0136	$164.01	$164.00	$164.00
Purchase #4	$33.29	13.544%	$37.7988	$37.80	$37.80	$37.80
Purchase #5	$29.95	5.170%	$31.4984	$31.50	$31.50	$31.50
Purchase #6	$156.71	5.179%	$164.826	$164.83	$164.85	$164.80
Purchase #7	$108.74	7.749%	$117.1663	$117.17	$117.15	$117.20
7 purchase totals =	$621.45		$672.2706	$672.28	$672.30	$672.30