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	$217.54	11.481%	$242.5158	$242.52	$242.50	$242.50
Purchase #2	$215.80	10.695%	$238.8798	$238.88	$238.90	$238.90
Purchase #3	$23.45	10.607%	$25.9373	$25.94	$25.95	$25.90
Purchase #4	$208.33	13.696%	$236.8629	$236.86	$236.85	$236.90
Purchase #5	$44.88	12.531%	$50.5039	$50.50	$50.50	$50.50
Purchase #6	$162.42	9.727%	$178.2186	$178.22	$178.20	$178.20
Purchase #7	$147.64	12.676%	$166.3548	$166.35	$166.35	$166.40
7 purchase totals =	$1,020.06		$1,139.2731	$1,139.27	$1,139.25	$1,139.30