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	$12.27	10.770%	$13.5915	$13.59	$13.60	$13.60
Purchase #2	$137.70	10.838%	$152.6239	$152.62	$152.60	$152.60
Purchase #3	$234.97	13.517%	$266.7309	$266.73	$266.75	$266.70
Purchase #4	$205.84	13.839%	$234.3262	$234.33	$234.35	$234.30
Purchase #5	$18.59	9.149%	$20.2908	$20.29	$20.30	$20.30
Purchase #6	$34.34	9.387%	$37.5635	$37.56	$37.55	$37.60
Purchase #7	$182.45	7.585%	$196.2888	$196.29	$196.30	$196.30
7 purchase totals =	$826.16		$921.4156	$921.41	$921.45	$921.40