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	$38.71	3.134%	$39.9232	$39.92	$39.90	$39.90
Purchase #2	$206.76	11.504%	$230.5457	$230.55	$230.55	$230.50
Purchase #3	$36.66	3.398%	$37.9057	$37.91	$37.90	$37.90
Purchase #4	$48.64	11.558%	$54.2618	$54.26	$54.25	$54.30
Purchase #5	$241.34	12.208%	$270.8028	$270.80	$270.80	$270.80
Purchase #6	$208.81	12.650%	$235.2245	$235.22	$235.20	$235.20
Purchase #7	$196.95	10.315%	$217.2654	$217.27	$217.25	$217.30
7 purchase totals =	$977.87		$1,085.9291	$1,085.93	$1,085.85	$1,085.90