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	$239.71	11.307%	$266.814	$266.81	$266.80	$266.80
Purchase #2	$148.40	5.524%	$156.5976	$156.60	$156.60	$156.60
Purchase #3	$213.51	7.347%	$229.1966	$229.20	$229.20	$229.20
Purchase #4	$33.86	6.269%	$35.9827	$35.98	$36.00	$36.00
Purchase #5	$18.67	9.540%	$20.4511	$20.45	$20.45	$20.50
Purchase #6	$106.71	12.711%	$120.2739	$120.27	$120.25	$120.30
Purchase #7	$133.61	11.418%	$148.8656	$148.87	$148.85	$148.90
7 purchase totals =	$894.47		$978.1815	$978.18	$978.15	$978.30