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	$87.56	13.644%	$99.5067	$99.51	$99.50	$99.50
Purchase #2	$106.38	10.184%	$117.2137	$117.21	$117.20	$117.20
Purchase #3	$176.47	6.416%	$187.7923	$187.79	$187.80	$187.80
Purchase #4	$151.95	6.871%	$162.3905	$162.39	$162.40	$162.40
Purchase #5	$93.70	12.836%	$105.7273	$105.73	$105.75	$105.70
Purchase #6	$210.29	9.662%	$230.6082	$230.61	$230.60	$230.60
Purchase #7	$216.42	3.314%	$223.5922	$223.59	$223.60	$223.60
7 purchase totals =	$1,042.77		$1,126.8309	$1,126.83	$1,126.85	$1,126.80