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	$108.53	7.319%	$116.4733	$116.47	$116.45	$116.50
Purchase #2	$213.97	11.517%	$238.6129	$238.61	$238.60	$238.60
Purchase #3	$229.77	3.150%	$237.0078	$237.01	$237.00	$237.00
Purchase #4	$178.83	3.535%	$185.1516	$185.15	$185.15	$185.20
Purchase #5	$51.65	13.329%	$58.5344	$58.53	$58.55	$58.50
Purchase #6	$20.56	8.298%	$22.2661	$22.27	$22.25	$22.30
Purchase #7	$240.92	11.719%	$269.1534	$269.15	$269.15	$269.20
7 purchase totals =	$1,044.23		$1,127.1995	$1,127.19	$1,127.15	$1,127.30