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	$56.65	5.146%	$59.5652	$59.57	$59.55	$59.60
Purchase #2	$33.45	10.439%	$36.9418	$36.94	$36.95	$36.90
Purchase #3	$90.28	6.784%	$96.4046	$96.40	$96.40	$96.40
Purchase #4	$73.95	12.870%	$83.4674	$83.47	$83.45	$83.50
Purchase #5	$234.71	10.757%	$259.9578	$259.96	$259.95	$260.00
Purchase #6	$78.87	13.380%	$89.4228	$89.42	$89.40	$89.40
Purchase #7	$203.81	6.105%	$216.2526	$216.25	$216.25	$216.30
7 purchase totals =	$771.72		$842.0122	$842.01	$841.95	$842.10