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	$19.47	3.409%	$20.1337	$20.13	$20.15	$20.10
Purchase #2	$234.97	12.158%	$263.5377	$263.54	$263.55	$263.50
Purchase #3	$165.81	13.242%	$187.7666	$187.77	$187.75	$187.80
Purchase #4	$130.80	7.396%	$140.474	$140.47	$140.45	$140.50
Purchase #5	$129.49	13.834%	$147.4036	$147.40	$147.40	$147.40
Purchase #6	$177.85	10.323%	$196.2095	$196.21	$196.20	$196.20
Purchase #7	$133.63	10.808%	$148.0727	$148.07	$148.05	$148.10
7 purchase totals =	$992.02		$1,103.5978	$1,103.59	$1,103.55	$1,103.60