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	$37.59	12.696%	$42.3624	$42.36	$42.35	$42.40
Purchase #2	$239.81	13.687%	$272.6328	$272.63	$272.65	$272.60
Purchase #3	$49.81	11.604%	$55.59	$55.59	$55.60	$55.60
Purchase #4	$84.39	13.684%	$95.9379	$95.94	$95.95	$95.90
Purchase #5	$101.90	11.470%	$113.5879	$113.59	$113.60	$113.60
Purchase #6	$45.88	4.795%	$48.0799	$48.08	$48.10	$48.10
Purchase #7	$208.59	3.811%	$216.5394	$216.54	$216.55	$216.50
7 purchase totals =	$767.97		$844.7303	$844.73	$844.80	$844.70