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	$202.52	6.377%	$215.4347	$215.43	$215.45	$215.40
Purchase #2	$35.30	13.842%	$40.1862	$40.19	$40.20	$40.20
Purchase #3	$192.68	3.224%	$198.892	$198.89	$198.90	$198.90
Purchase #4	$206.38	7.257%	$221.357	$221.36	$221.35	$221.40
Purchase #5	$153.82	8.248%	$166.5071	$166.51	$166.50	$166.50
Purchase #6	$24.52	10.182%	$27.0166	$27.02	$27.00	$27.00
Purchase #7	$40.32	12.768%	$45.4681	$45.47	$45.45	$45.50
7 purchase totals =	$855.54		$914.8617	$914.87	$914.85	$914.90