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	$156.91	12.691%	$176.8234	$176.82	$176.80	$176.80
Purchase #2	$132.90	9.145%	$145.0537	$145.05	$145.05	$145.10
Purchase #3	$149.72	3.835%	$155.4618	$155.46	$155.45	$155.50
Purchase #4	$199.89	6.784%	$213.4505	$213.45	$213.45	$213.50
Purchase #5	$83.26	7.595%	$89.5836	$89.58	$89.60	$89.60
Purchase #6	$41.83	5.515%	$44.1369	$44.14	$44.15	$44.10
Purchase #7	$15.83	13.136%	$17.9094	$17.91	$17.90	$17.90
7 purchase totals =	$780.34		$842.4193	$842.41	$842.40	$842.50