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	$104.27	3.329%	$107.7411	$107.74	$107.75	$107.70
Purchase #2	$61.52	13.423%	$69.7778	$69.78	$69.80	$69.80
Purchase #3	$224.83	11.541%	$250.7776	$250.78	$250.80	$250.80
Purchase #4	$199.52	13.209%	$225.8746	$225.87	$225.85	$225.90
Purchase #5	$99.84	12.741%	$112.5606	$112.56	$112.55	$112.60
Purchase #6	$117.44	11.665%	$131.1394	$131.14	$131.15	$131.10
Purchase #7	$70.32	10.381%	$77.6199	$77.62	$77.60	$77.60
7 purchase totals =	$877.74		$975.4910	$975.49	$975.50	$975.50