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	$166.77	13.140%	$188.6836	$188.68	$188.70	$188.70
Purchase #2	$145.26	8.633%	$157.8003	$157.80	$157.80	$157.80
Purchase #3	$89.86	12.338%	$100.9469	$100.95	$100.95	$100.90
Purchase #4	$185.72	12.294%	$208.5524	$208.55	$208.55	$208.60
Purchase #5	$118.64	4.499%	$123.9776	$123.98	$124.00	$124.00
Purchase #6	$35.37	6.825%	$37.784	$37.78	$37.80	$37.80
Purchase #7	$14.80	4.829%	$15.5147	$15.51	$15.50	$15.50
7 purchase totals =	$756.42		$833.2595	$833.25	$833.30	$833.30