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	$245.95	10.780%	$272.4634	$272.46	$272.45	$272.50
Purchase #2	$104.75	9.330%	$114.5232	$114.52	$114.50	$114.50
Purchase #3	$131.95	13.318%	$149.5231	$149.52	$149.50	$149.50
Purchase #4	$158.61	8.680%	$172.3773	$172.38	$172.40	$172.40
Purchase #5	$196.83	12.500%	$221.4338	$221.43	$221.45	$221.40
Purchase #6	$132.95	8.579%	$144.3558	$144.36	$144.35	$144.40
Purchase #7	$16.55	9.661%	$18.1489	$18.15	$18.15	$18.10
7 purchase totals =	$987.59		$1,092.8255	$1,092.82	$1,092.80	$1,092.80