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	$103.92	4.128%	$108.2098	$108.21	$108.20	$108.20
Purchase #2	$107.83	10.604%	$119.2643	$119.26	$119.25	$119.30
Purchase #3	$228.96	3.307%	$236.5317	$236.53	$236.55	$236.50
Purchase #4	$150.65	13.737%	$171.3448	$171.34	$171.35	$171.30
Purchase #5	$51.29	5.801%	$54.2653	$54.27	$54.25	$54.30
Purchase #6	$59.43	11.527%	$66.2805	$66.28	$66.30	$66.30
Purchase #7	$189.43	5.867%	$200.5439	$200.54	$200.55	$200.50
7 purchase totals =	$891.51		$956.4403	$956.43	$956.45	$956.40