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	$235.65	12.307%	$264.6514	$264.65	$264.65	$264.70
Purchase #2	$83.98	8.159%	$90.8319	$90.83	$90.85	$90.80
Purchase #3	$214.58	7.780%	$231.2743	$231.27	$231.25	$231.30
Purchase #4	$196.43	4.781%	$205.8213	$205.82	$205.80	$205.80
Purchase #5	$21.64	4.588%	$22.6328	$22.63	$22.65	$22.60
Purchase #6	$64.51	3.792%	$66.9562	$66.96	$66.95	$67.00
Purchase #7	$147.45	5.849%	$156.0744	$156.07	$156.05	$156.10
7 purchase totals =	$964.24		$1,038.2423	$1,038.23	$1,038.20	$1,038.30