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	$69.92	12.105%	$78.3838	$78.38	$78.40	$78.40
Purchase #2	$164.27	7.199%	$176.0958	$176.10	$176.10	$176.10
Purchase #3	$41.89	13.294%	$47.4589	$47.46	$47.45	$47.50
Purchase #4	$13.49	12.810%	$15.2181	$15.22	$15.20	$15.20
Purchase #5	$43.57	3.622%	$45.1481	$45.15	$45.15	$45.10
Purchase #6	$152.55	6.761%	$162.8639	$162.86	$162.85	$162.90
Purchase #7	$132.46	3.720%	$137.3875	$137.39	$137.40	$137.40
7 purchase totals =	$618.15		$662.5561	$662.56	$662.55	$662.60