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	$250.43	11.687%	$279.6978	$279.70	$279.70	$279.70
Purchase #2	$145.66	11.410%	$162.2798	$162.28	$162.30	$162.30
Purchase #3	$62.89	11.326%	$70.0129	$70.01	$70.00	$70.00
Purchase #4	$32.96	11.753%	$36.8338	$36.83	$36.85	$36.80
Purchase #5	$194.57	10.540%	$215.0777	$215.08	$215.10	$215.10
Purchase #6	$223.46	8.233%	$241.8575	$241.86	$241.85	$241.90
Purchase #7	$148.28	4.253%	$154.5863	$154.59	$154.60	$154.60
7 purchase totals =	$1,058.25		$1,160.3458	$1,160.35	$1,160.40	$1,160.40