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	$17.82	3.338%	$18.4148	$18.41	$18.40	$18.40
Purchase #2	$141.53	13.162%	$160.1582	$160.16	$160.15	$160.20
Purchase #3	$166.63	12.426%	$187.3354	$187.34	$187.35	$187.30
Purchase #4	$17.96	9.141%	$19.6017	$19.60	$19.60	$19.60
Purchase #5	$100.25	3.212%	$103.47	$103.47	$103.45	$103.50
Purchase #6	$138.48	9.622%	$151.8045	$151.80	$151.80	$151.80
Purchase #7	$139.65	8.589%	$151.6445	$151.64	$151.65	$151.60
7 purchase totals =	$722.32		$792.4291	$792.42	$792.40	$792.40