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	$104.36	13.733%	$118.6918	$118.69	$118.70	$118.70
Purchase #2	$153.58	10.602%	$169.8626	$169.86	$169.85	$169.90
Purchase #3	$172.30	9.822%	$189.2233	$189.22	$189.20	$189.20
Purchase #4	$68.93	13.314%	$78.1073	$78.11	$78.10	$78.10
Purchase #5	$88.36	6.533%	$94.1326	$94.13	$94.15	$94.10
Purchase #6	$83.70	7.160%	$89.6929	$89.69	$89.70	$89.70
Purchase #7	$112.38	10.827%	$124.5474	$124.55	$124.55	$124.50
7 purchase totals =	$783.61		$864.2579	$864.25	$864.25	$864.20