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	$179.78	9.794%	$197.3877	$197.39	$197.40	$197.40
Purchase #2	$73.43	10.134%	$80.8714	$80.87	$80.85	$80.90
Purchase #3	$72.97	4.732%	$76.4229	$76.42	$76.40	$76.40
Purchase #4	$122.98	4.526%	$128.5461	$128.55	$128.55	$128.50
Purchase #5	$44.56	11.858%	$49.8439	$49.84	$49.85	$49.80
Purchase #6	$107.88	3.617%	$111.782	$111.78	$111.80	$111.80
Purchase #7	$37.60	12.531%	$42.3117	$42.31	$42.30	$42.30
7 purchase totals =	$639.20		$687.1657	$687.16	$687.15	$687.10