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	$243.52	5.229%	$256.2537	$256.25	$256.25	$256.30
Purchase #2	$43.34	11.796%	$48.4524	$48.45	$48.45	$48.50
Purchase #3	$182.97	7.337%	$196.3945	$196.39	$196.40	$196.40
Purchase #4	$127.51	5.721%	$134.8048	$134.80	$134.80	$134.80
Purchase #5	$159.77	13.170%	$180.8117	$180.81	$180.80	$180.80
Purchase #6	$96.63	12.200%	$108.4189	$108.42	$108.40	$108.40
Purchase #7	$45.55	10.811%	$50.4744	$50.47	$50.45	$50.50
7 purchase totals =	$899.29		$975.6104	$975.59	$975.55	$975.70