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	$82.56	6.517%	$87.9404	$87.94	$87.95	$87.90
Purchase #2	$150.40	5.363%	$158.466	$158.47	$158.45	$158.50
Purchase #3	$137.25	10.178%	$151.2193	$151.22	$151.20	$151.20
Purchase #4	$101.68	7.402%	$109.2064	$109.21	$109.20	$109.20
Purchase #5	$96.79	3.866%	$100.5319	$100.53	$100.55	$100.50
Purchase #6	$16.34	4.554%	$17.0841	$17.08	$17.10	$17.10
Purchase #7	$38.69	4.790%	$40.5433	$40.54	$40.55	$40.50
7 purchase totals =	$623.71		$664.9914	$664.99	$665.00	$664.90