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	$136.51	7.178%	$146.3087	$146.31	$146.30	$146.30
Purchase #2	$110.85	4.217%	$115.5245	$115.52	$115.50	$115.50
Purchase #3	$189.88	3.617%	$196.748	$196.75	$196.75	$196.70
Purchase #4	$132.51	13.271%	$150.0954	$150.10	$150.10	$150.10
Purchase #5	$107.98	8.318%	$116.9618	$116.96	$116.95	$117.00
Purchase #6	$49.38	4.218%	$51.4628	$51.46	$51.45	$51.50
Purchase #7	$151.83	13.849%	$172.8569	$172.86	$172.85	$172.90
7 purchase totals =	$878.94		$949.9581	$949.96	$949.90	$950.00