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	$163.34	11.172%	$181.5883	$181.59	$181.60	$181.60
Purchase #2	$210.27	13.459%	$238.5702	$238.57	$238.55	$238.60
Purchase #3	$109.93	8.185%	$118.9278	$118.93	$118.95	$118.90
Purchase #4	$68.39	4.466%	$71.4443	$71.44	$71.45	$71.40
Purchase #5	$94.93	6.507%	$101.1071	$101.11	$101.10	$101.10
Purchase #6	$103.70	10.774%	$114.8726	$114.87	$114.85	$114.90
Purchase #7	$148.57	12.375%	$166.9555	$166.96	$166.95	$167.00
7 purchase totals =	$899.13		$993.4658	$993.47	$993.45	$993.50