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	$33.47	7.270%	$35.9033	$35.90	$35.90	$35.90
Purchase #2	$191.62	3.353%	$198.045	$198.05	$198.05	$198.00
Purchase #3	$227.40	6.154%	$241.3942	$241.39	$241.40	$241.40
Purchase #4	$73.64	13.771%	$83.781	$83.78	$83.80	$83.80
Purchase #5	$63.83	13.616%	$72.5211	$72.52	$72.50	$72.50
Purchase #6	$227.95	13.110%	$257.8342	$257.83	$257.85	$257.80
Purchase #7	$117.28	12.610%	$132.069	$132.07	$132.05	$132.10
7 purchase totals =	$935.19		$1,021.5478	$1,021.54	$1,021.55	$1,021.50