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	$42.68	6.619%	$45.505	$45.51	$45.50	$45.50
Purchase #2	$162.42	9.174%	$177.3204	$177.32	$177.30	$177.30
Purchase #3	$176.54	11.129%	$196.1871	$196.19	$196.20	$196.20
Purchase #4	$162.35	3.813%	$168.5404	$168.54	$168.55	$168.50
Purchase #5	$54.85	12.393%	$61.6476	$61.65	$61.65	$61.60
Purchase #6	$199.57	3.217%	$205.9902	$205.99	$206.00	$206.00
Purchase #7	$118.95	6.189%	$126.3118	$126.31	$126.30	$126.30
7 purchase totals =	$917.36		$981.5025	$981.51	$981.50	$981.40