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	$129.61	8.344%	$140.4247	$140.42	$140.40	$140.40
Purchase #2	$37.50	11.268%	$41.7255	$41.73	$41.75	$41.70
Purchase #3	$71.71	13.722%	$81.55	$81.55	$81.55	$81.60
Purchase #4	$231.25	12.140%	$259.3238	$259.32	$259.30	$259.30
Purchase #5	$186.52	5.411%	$196.6126	$196.61	$196.60	$196.60
Purchase #6	$103.38	13.252%	$117.0799	$117.08	$117.10	$117.10
Purchase #7	$6.38	13.824%	$7.262	$7.26	$7.25	$7.30
7 purchase totals =	$766.35		$843.9785	$843.97	$843.95	$844.00