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	$146.39	6.833%	$156.3928	$156.39	$156.40	$156.40
Purchase #2	$22.37	9.178%	$24.4231	$24.42	$24.40	$24.40
Purchase #3	$61.33	6.723%	$65.4532	$65.45	$65.45	$65.50
Purchase #4	$235.64	10.275%	$259.852	$259.85	$259.85	$259.90
Purchase #5	$27.28	7.525%	$29.3328	$29.33	$29.35	$29.30
Purchase #6	$219.46	9.549%	$240.4162	$240.42	$240.40	$240.40
Purchase #7	$199.63	13.768%	$227.1151	$227.12	$227.10	$227.10
7 purchase totals =	$912.10		$1,002.9852	$1,002.98	$1,002.95	$1,003.00