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	$105.84	10.238%	$116.6759	$116.68	$116.70	$116.70
Purchase #2	$51.86	4.590%	$54.2404	$54.24	$54.25	$54.20
Purchase #3	$211.32	9.537%	$231.4736	$231.47	$231.45	$231.50
Purchase #4	$59.29	11.270%	$65.972	$65.97	$65.95	$66.00
Purchase #5	$166.30	11.796%	$185.9167	$185.92	$185.90	$185.90
Purchase #6	$105.41	8.629%	$114.5058	$114.51	$114.50	$114.50
Purchase #7	$15.85	13.164%	$17.9365	$17.94	$17.95	$17.90
7 purchase totals =	$715.87		$786.7209	$786.73	$786.70	$786.70