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	$37.98	12.264%	$42.6379	$42.64	$42.65	$42.60
Purchase #2	$30.82	3.120%	$31.7816	$31.78	$31.80	$31.80
Purchase #3	$187.59	11.342%	$208.8665	$208.87	$208.85	$208.90
Purchase #4	$52.87	12.408%	$59.4301	$59.43	$59.45	$59.40
Purchase #5	$136.25	6.700%	$145.3788	$145.38	$145.40	$145.40
Purchase #6	$216.70	13.557%	$246.078	$246.08	$246.10	$246.10
Purchase #7	$56.58	7.240%	$60.6764	$60.68	$60.70	$60.70
7 purchase totals =	$718.79		$794.8493	$794.86	$794.95	$794.90