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	$21.71	7.329%	$23.3011	$23.30	$23.30	$23.30
Purchase #2	$74.87	10.406%	$82.661	$82.66	$82.65	$82.70
Purchase #3	$198.65	7.480%	$213.509	$213.51	$213.50	$213.50
Purchase #4	$70.47	10.557%	$77.9095	$77.91	$77.90	$77.90
Purchase #5	$49.38	6.128%	$52.406	$52.41	$52.40	$52.40
Purchase #6	$171.40	11.158%	$190.5248	$190.52	$190.50	$190.50
Purchase #7	$8.35	3.176%	$8.6152	$8.62	$8.60	$8.60
7 purchase totals =	$594.83		$648.9266	$648.93	$648.85	$648.90