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	$103.68	5.509%	$109.3917	$109.39	$109.40	$109.40
Purchase #2	$172.62	13.760%	$196.3725	$196.37	$196.35	$196.40
Purchase #3	$170.48	9.835%	$187.2467	$187.25	$187.25	$187.20
Purchase #4	$145.47	7.498%	$156.3773	$156.38	$156.40	$156.40
Purchase #5	$148.90	4.655%	$155.8313	$155.83	$155.85	$155.80
Purchase #6	$39.25	6.539%	$41.8166	$41.82	$41.80	$41.80
Purchase #7	$40.45	8.177%	$43.7576	$43.76	$43.75	$43.80
7 purchase totals =	$820.85		$890.7937	$890.80	$890.80	$890.80