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	$50.99	7.252%	$54.6878	$54.69	$54.70	$54.70
Purchase #2	$149.81	12.714%	$168.8568	$168.86	$168.85	$168.90
Purchase #3	$174.47	12.397%	$196.099	$196.10	$196.10	$196.10
Purchase #4	$19.81	10.842%	$21.9578	$21.96	$21.95	$22.00
Purchase #5	$67.49	12.725%	$76.0781	$76.08	$76.10	$76.10
Purchase #6	$10.57	11.620%	$11.7982	$11.80	$11.80	$11.80
Purchase #7	$127.59	8.363%	$138.2604	$138.26	$138.25	$138.30
7 purchase totals =	$600.73		$667.7381	$667.75	$667.75	$667.90