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	$53.25	4.584%	$55.691	$55.69	$55.70	$55.70
Purchase #2	$104.84	8.396%	$113.6424	$113.64	$113.65	$113.60
Purchase #3	$18.30	12.211%	$20.5346	$20.53	$20.55	$20.50
Purchase #4	$224.49	13.861%	$255.6066	$255.61	$255.60	$255.60
Purchase #5	$153.88	9.190%	$168.0216	$168.02	$168.00	$168.00
Purchase #6	$184.39	10.829%	$204.3576	$204.36	$204.35	$204.40
Purchase #7	$37.45	8.260%	$40.5434	$40.54	$40.55	$40.50
7 purchase totals =	$776.60		$858.3972	$858.39	$858.40	$858.30