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	$21.45	4.287%	$22.3696	$22.37	$22.35	$22.40
Purchase #2	$69.38	10.866%	$76.9188	$76.92	$76.90	$76.90
Purchase #3	$19.92	3.520%	$20.6212	$20.62	$20.60	$20.60
Purchase #4	$146.65	6.656%	$156.411	$156.41	$156.40	$156.40
Purchase #5	$137.56	6.239%	$146.1424	$146.14	$146.15	$146.10
Purchase #6	$18.93	6.331%	$20.1285	$20.13	$20.15	$20.10
Purchase #7	$227.87	4.688%	$238.5525	$238.55	$238.55	$238.60
7 purchase totals =	$641.76		$681.1440	$681.14	$681.10	$681.10