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	$82.74	4.269%	$86.2722	$86.27	$86.25	$86.30
Purchase #2	$175.74	5.421%	$185.2669	$185.27	$185.25	$185.30
Purchase #3	$64.88	8.344%	$70.2936	$70.29	$70.30	$70.30
Purchase #4	$126.32	6.151%	$134.0899	$134.09	$134.10	$134.10
Purchase #5	$118.72	3.832%	$123.2694	$123.27	$123.25	$123.30
Purchase #6	$32.93	3.193%	$33.9815	$33.98	$34.00	$34.00
Purchase #7	$145.86	11.652%	$162.8556	$162.86	$162.85	$162.90
7 purchase totals =	$747.19		$796.0291	$796.03	$796.00	$796.20