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	$38.31	6.533%	$40.8128	$40.81	$40.80	$40.80
Purchase #2	$50.56	6.382%	$53.7867	$53.79	$53.80	$53.80
Purchase #3	$97.35	10.523%	$107.5941	$107.59	$107.60	$107.60
Purchase #4	$153.58	8.470%	$166.5882	$166.59	$166.60	$166.60
Purchase #5	$83.61	8.741%	$90.9184	$90.92	$90.90	$90.90
Purchase #6	$91.33	9.665%	$100.157	$100.16	$100.15	$100.20
Purchase #7	$101.53	10.682%	$112.3754	$112.38	$112.40	$112.40
7 purchase totals =	$616.27		$672.2326	$672.24	$672.25	$672.30