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	$244.59	9.687%	$268.2834	$268.28	$268.30	$268.30
Purchase #2	$17.65	10.766%	$19.5502	$19.55	$19.55	$19.60
Purchase #3	$125.48	10.837%	$139.0783	$139.08	$139.10	$139.10
Purchase #4	$220.53	5.123%	$231.8278	$231.83	$231.85	$231.80
Purchase #5	$88.85	13.405%	$100.7603	$100.76	$100.75	$100.80
Purchase #6	$237.34	9.538%	$259.9775	$259.98	$260.00	$260.00
Purchase #7	$94.28	4.786%	$98.7922	$98.79	$98.80	$98.80
7 purchase totals =	$1,028.72		$1,118.2697	$1,118.27	$1,118.35	$1,118.40