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	$77.71	3.856%	$80.7065	$80.71	$80.70	$80.70
Purchase #2	$164.48	12.709%	$185.3838	$185.38	$185.40	$185.40
Purchase #3	$58.52	5.845%	$61.9405	$61.94	$61.95	$61.90
Purchase #4	$65.53	13.648%	$74.4735	$74.47	$74.45	$74.50
Purchase #5	$111.99	13.596%	$127.2162	$127.22	$127.20	$127.20
Purchase #6	$198.69	9.635%	$217.8338	$217.83	$217.85	$217.80
Purchase #7	$68.99	10.830%	$76.4616	$76.46	$76.45	$76.50
7 purchase totals =	$745.91		$824.0159	$824.01	$824.00	$824.00