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	$212.78	12.587%	$239.5626	$239.56	$239.55	$239.60
Purchase #2	$129.59	10.806%	$143.5935	$143.59	$143.60	$143.60
Purchase #3	$200.48	13.365%	$227.2742	$227.27	$227.25	$227.30
Purchase #4	$39.59	9.644%	$43.4081	$43.41	$43.40	$43.40
Purchase #5	$72.30	12.742%	$81.5125	$81.51	$81.50	$81.50
Purchase #6	$152.81	8.465%	$165.7454	$165.75	$165.75	$165.70
Purchase #7	$151.90	7.133%	$162.735	$162.74	$162.75	$162.70
7 purchase totals =	$959.45		$1,063.8313	$1,063.83	$1,063.80	$1,063.80