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	$55.42	6.583%	$59.0683	$59.07	$59.05	$59.10
Purchase #2	$87.51	3.440%	$90.5203	$90.52	$90.50	$90.50
Purchase #3	$24.93	11.129%	$27.7045	$27.70	$27.70	$27.70
Purchase #4	$41.35	10.558%	$45.7157	$45.72	$45.70	$45.70
Purchase #5	$116.59	10.248%	$128.5381	$128.54	$128.55	$128.50
Purchase #6	$140.34	3.262%	$144.9179	$144.92	$144.90	$144.90
Purchase #7	$48.36	7.777%	$52.121	$52.12	$52.10	$52.10
7 purchase totals =	$514.50		$548.5858	$548.59	$548.50	$548.50