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	$24.78	10.465%	$27.3732	$27.37	$27.35	$27.40
Purchase #2	$172.43	10.841%	$191.1231	$191.12	$191.10	$191.10
Purchase #3	$172.90	6.493%	$184.1264	$184.13	$184.15	$184.10
Purchase #4	$29.80	10.768%	$33.0089	$33.01	$33.00	$33.00
Purchase #5	$227.94	10.387%	$251.6161	$251.62	$251.60	$251.60
Purchase #6	$161.39	12.547%	$181.6396	$181.64	$181.65	$181.60
Purchase #7	$40.92	6.528%	$43.5913	$43.59	$43.60	$43.60
7 purchase totals =	$830.16		$912.4786	$912.48	$912.45	$912.40