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	$91.60	8.674%	$99.5454	$99.55	$99.55	$99.50
Purchase #2	$124.56	10.678%	$137.8605	$137.86	$137.85	$137.90
Purchase #3	$136.47	3.500%	$141.2465	$141.25	$141.25	$141.20
Purchase #4	$173.69	4.313%	$181.1812	$181.18	$181.20	$181.20
Purchase #5	$10.89	6.673%	$11.6167	$11.62	$11.60	$11.60
Purchase #6	$148.37	9.770%	$162.8657	$162.87	$162.85	$162.90
Purchase #7	$113.91	11.660%	$127.1919	$127.19	$127.20	$127.20
7 purchase totals =	$799.49		$861.5079	$861.52	$861.50	$861.50