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	$28.85	8.817%	$31.3937	$31.39	$31.40	$31.40
Purchase #2	$234.33	12.600%	$263.8556	$263.86	$263.85	$263.90
Purchase #3	$177.76	7.350%	$190.8254	$190.83	$190.85	$190.80
Purchase #4	$235.46	11.526%	$262.5991	$262.60	$262.60	$262.60
Purchase #5	$72.56	8.578%	$78.7842	$78.78	$78.80	$78.80
Purchase #6	$75.56	8.295%	$81.8277	$81.83	$81.85	$81.80
Purchase #7	$97.25	10.632%	$107.5896	$107.59	$107.60	$107.60
7 purchase totals =	$921.77		$1,016.8753	$1,016.88	$1,016.95	$1,016.90