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	$59.60	4.787%	$62.4531	$62.45	$62.45	$62.50
Purchase #2	$212.52	5.503%	$224.215	$224.22	$224.20	$224.20
Purchase #3	$212.65	10.705%	$235.4142	$235.41	$235.40	$235.40
Purchase #4	$95.95	4.143%	$99.9252	$99.93	$99.95	$99.90
Purchase #5	$75.65	10.358%	$83.4858	$83.49	$83.50	$83.50
Purchase #6	$81.59	7.783%	$87.9401	$87.94	$87.95	$87.90
Purchase #7	$169.60	9.260%	$185.305	$185.31	$185.30	$185.30
7 purchase totals =	$907.56		$978.7384	$978.75	$978.75	$978.70