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	$14.86	6.173%	$15.7773	$15.78	$15.80	$15.80
Purchase #2	$87.66	13.626%	$99.6046	$99.60	$99.60	$99.60
Purchase #3	$90.52	10.663%	$100.1721	$100.17	$100.15	$100.20
Purchase #4	$156.92	3.358%	$162.1894	$162.19	$162.20	$162.20
Purchase #5	$160.74	10.287%	$177.2753	$177.28	$177.30	$177.30
Purchase #6	$134.56	13.732%	$153.0378	$153.04	$153.05	$153.00
Purchase #7	$107.90	10.829%	$119.5845	$119.58	$119.60	$119.60
7 purchase totals =	$753.16		$827.6410	$827.64	$827.70	$827.70