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	$160.45	12.716%	$180.8528	$180.85	$180.85	$180.90
Purchase #2	$60.25	9.210%	$65.799	$65.80	$65.80	$65.80
Purchase #3	$40.74	11.656%	$45.4887	$45.49	$45.50	$45.50
Purchase #4	$11.51	3.781%	$11.9452	$11.95	$11.95	$11.90
Purchase #5	$75.69	4.143%	$78.8258	$78.83	$78.85	$78.80
Purchase #6	$62.65	5.104%	$65.8477	$65.85	$65.85	$65.80
Purchase #7	$249.30	9.761%	$273.6342	$273.63	$273.65	$273.60
7 purchase totals =	$660.59		$722.3934	$722.40	$722.45	$722.30