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	$242.38	6.540%	$258.2317	$258.23	$258.25	$258.20
Purchase #2	$48.64	9.865%	$53.4383	$53.44	$53.45	$53.40
Purchase #3	$16.94	6.488%	$18.0391	$18.04	$18.05	$18.00
Purchase #4	$58.55	6.630%	$62.4319	$62.43	$62.45	$62.40
Purchase #5	$19.47	11.863%	$21.7797	$21.78	$21.80	$21.80
Purchase #6	$69.28	12.834%	$78.1714	$78.17	$78.15	$78.20
Purchase #7	$20.59	4.169%	$21.4484	$21.45	$21.45	$21.40
7 purchase totals =	$475.85		$513.5405	$513.54	$513.60	$513.40