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	$208.31	3.632%	$215.8758	$215.88	$215.90	$215.90
Purchase #2	$81.97	10.533%	$90.6039	$90.60	$90.60	$90.60
Purchase #3	$70.33	7.753%	$75.7827	$75.78	$75.80	$75.80
Purchase #4	$18.35	7.433%	$19.714	$19.71	$19.70	$19.70
Purchase #5	$149.72	13.484%	$169.9082	$169.91	$169.90	$169.90
Purchase #6	$68.46	6.417%	$72.8531	$72.85	$72.85	$72.90
Purchase #7	$19.42	3.750%	$20.1483	$20.15	$20.15	$20.10
7 purchase totals =	$616.56		$664.8860	$664.88	$664.90	$664.90