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	$143.59	8.179%	$155.3342	$155.33	$155.35	$155.30
Purchase #2	$184.49	6.454%	$196.397	$196.40	$196.40	$196.40
Purchase #3	$39.40	3.668%	$40.8452	$40.85	$40.85	$40.80
Purchase #4	$24.55	5.627%	$25.9314	$25.93	$25.95	$25.90
Purchase #5	$37.47	5.861%	$39.6661	$39.67	$39.65	$39.70
Purchase #6	$97.39	10.454%	$107.5712	$107.57	$107.55	$107.60
Purchase #7	$41.83	7.800%	$45.0927	$45.09	$45.10	$45.10
7 purchase totals =	$568.72		$610.8378	$610.84	$610.85	$610.80