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	$37.35	9.159%	$40.7709	$40.77	$40.75	$40.80
Purchase #2	$186.55	7.144%	$199.8771	$199.88	$199.90	$199.90
Purchase #3	$27.79	7.595%	$29.9007	$29.90	$29.90	$29.90
Purchase #4	$43.54	3.178%	$44.9237	$44.92	$44.90	$44.90
Purchase #5	$78.33	3.752%	$81.2689	$81.27	$81.25	$81.30
Purchase #6	$52.35	3.748%	$54.3121	$54.31	$54.30	$54.30
Purchase #7	$236.28	4.298%	$246.4353	$246.44	$246.45	$246.40
7 purchase totals =	$662.19		$697.4887	$697.49	$697.45	$697.50