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	$87.47	13.236%	$99.0475	$99.05	$99.05	$99.00
Purchase #2	$177.65	10.479%	$196.2659	$196.27	$196.25	$196.30
Purchase #3	$169.65	5.820%	$179.5236	$179.52	$179.50	$179.50
Purchase #4	$105.97	12.224%	$118.9238	$118.92	$118.90	$118.90
Purchase #5	$150.45	11.828%	$168.2452	$168.25	$168.25	$168.20
Purchase #6	$23.76	7.838%	$25.6223	$25.62	$25.60	$25.60
Purchase #7	$148.35	7.605%	$159.632	$159.63	$159.65	$159.60
7 purchase totals =	$863.30		$947.2603	$947.26	$947.20	$947.10