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	$134.91	6.380%	$143.5173	$143.52	$143.50	$143.50
Purchase #2	$18.72	13.379%	$21.2245	$21.22	$21.20	$21.20
Purchase #3	$179.97	3.330%	$185.963	$185.96	$185.95	$186.00
Purchase #4	$41.33	3.264%	$42.679	$42.68	$42.70	$42.70
Purchase #5	$121.41	10.309%	$133.9262	$133.93	$133.95	$133.90
Purchase #6	$95.33	10.746%	$105.5742	$105.57	$105.55	$105.60
Purchase #7	$46.68	4.651%	$48.8511	$48.85	$48.85	$48.90
7 purchase totals =	$638.35		$681.7353	$681.73	$681.70	$681.80