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	$57.78	8.776%	$62.8508	$62.85	$62.85	$62.90
Purchase #2	$180.45	8.733%	$196.2087	$196.21	$196.20	$196.20
Purchase #3	$62.31	6.492%	$66.3552	$66.36	$66.35	$66.40
Purchase #4	$169.80	9.240%	$185.4895	$185.49	$185.50	$185.50
Purchase #5	$15.59	11.176%	$17.3323	$17.33	$17.35	$17.30
Purchase #6	$116.47	8.190%	$126.0089	$126.01	$126.00	$126.00
Purchase #7	$171.29	4.673%	$179.2944	$179.29	$179.30	$179.30
7 purchase totals =	$773.69		$833.5398	$833.54	$833.55	$833.60