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	$192.54	13.174%	$217.9052	$217.91	$217.90	$217.90
Purchase #2	$54.28	12.704%	$61.1757	$61.18	$61.20	$61.20
Purchase #3	$166.40	11.710%	$185.8854	$185.89	$185.90	$185.90
Purchase #4	$11.48	3.207%	$11.8482	$11.85	$11.85	$11.80
Purchase #5	$96.84	5.149%	$101.8263	$101.83	$101.85	$101.80
Purchase #6	$166.31	7.176%	$178.2444	$178.24	$178.25	$178.20
Purchase #7	$104.62	4.422%	$109.2463	$109.25	$109.25	$109.20
7 purchase totals =	$792.47		$866.1315	$866.15	$866.20	$866.00