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	$233.30	12.846%	$263.2697	$263.27	$263.25	$263.30
Purchase #2	$57.41	6.503%	$61.1434	$61.14	$61.15	$61.10
Purchase #3	$93.62	12.666%	$105.4779	$105.48	$105.50	$105.50
Purchase #4	$103.42	8.796%	$112.5168	$112.52	$112.50	$112.50
Purchase #5	$16.83	4.445%	$17.5781	$17.58	$17.60	$17.60
Purchase #6	$133.46	7.798%	$143.8672	$143.87	$143.85	$143.90
Purchase #7	$51.90	9.626%	$56.8959	$56.90	$56.90	$56.90
7 purchase totals =	$689.94		$760.7490	$760.76	$760.75	$760.80