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	$25.82	6.600%	$27.5241	$27.52	$27.50	$27.50
Purchase #2	$108.31	13.748%	$123.2005	$123.20	$123.20	$123.20
Purchase #3	$231.83	13.708%	$263.6093	$263.61	$263.60	$263.60
Purchase #4	$213.33	13.449%	$242.0208	$242.02	$242.00	$242.00
Purchase #5	$95.35	8.640%	$103.5882	$103.59	$103.60	$103.60
Purchase #6	$51.59	5.828%	$54.5967	$54.60	$54.60	$54.60
Purchase #7	$6.66	5.177%	$7.0048	$7.00	$7.00	$7.00
7 purchase totals =	$732.89		$821.5444	$821.54	$821.50	$821.50