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	$52.86	5.592%	$55.8159	$55.82	$55.80	$55.80
Purchase #2	$163.90	9.789%	$179.9442	$179.94	$179.95	$179.90
Purchase #3	$70.47	3.630%	$73.0281	$73.03	$73.05	$73.00
Purchase #4	$88.55	10.584%	$97.9221	$97.92	$97.90	$97.90
Purchase #5	$136.78	6.241%	$145.3164	$145.32	$145.30	$145.30
Purchase #6	$54.41	4.662%	$56.9466	$56.95	$56.95	$56.90
Purchase #7	$233.34	13.392%	$264.5889	$264.59	$264.60	$264.60
7 purchase totals =	$800.31		$873.5622	$873.57	$873.55	$873.40