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	$82.69	7.636%	$89.0042	$89.00	$89.00	$89.00
Purchase #2	$120.91	6.575%	$128.8598	$128.86	$128.85	$128.90
Purchase #3	$23.74	3.701%	$24.6186	$24.62	$24.60	$24.60
Purchase #4	$232.90	3.779%	$241.7013	$241.70	$241.70	$241.70
Purchase #5	$31.64	6.584%	$33.7232	$33.72	$33.70	$33.70
Purchase #6	$160.70	7.309%	$172.4456	$172.45	$172.45	$172.40
Purchase #7	$29.83	9.451%	$32.6492	$32.65	$32.65	$32.60
7 purchase totals =	$682.41		$723.0019	$723.00	$722.95	$722.90