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	$40.36	12.481%	$45.3973	$45.40	$45.40	$45.40
Purchase #2	$183.65	7.795%	$197.9655	$197.97	$197.95	$198.00
Purchase #3	$128.43	5.850%	$135.9432	$135.94	$135.95	$135.90
Purchase #4	$186.44	5.242%	$196.2132	$196.21	$196.20	$196.20
Purchase #5	$137.77	9.206%	$150.4531	$150.45	$150.45	$150.50
Purchase #6	$36.76	10.411%	$40.5871	$40.59	$40.60	$40.60
Purchase #7	$43.25	11.609%	$48.2709	$48.27	$48.25	$48.30
7 purchase totals =	$756.66		$814.8303	$814.83	$814.80	$814.90