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	$231.98	4.241%	$241.8183	$241.82	$241.80	$241.80
Purchase #2	$168.89	9.816%	$185.4682	$185.47	$185.45	$185.50
Purchase #3	$82.70	8.805%	$89.9817	$89.98	$90.00	$90.00
Purchase #4	$15.89	3.703%	$16.4784	$16.48	$16.50	$16.50
Purchase #5	$196.88	5.624%	$207.9525	$207.95	$207.95	$208.00
Purchase #6	$238.86	11.426%	$266.1521	$266.15	$266.15	$266.20
Purchase #7	$226.93	13.765%	$258.1669	$258.17	$258.15	$258.20
7 purchase totals =	$1,162.13		$1,266.0181	$1,266.02	$1,266.00	$1,266.20