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	$78.43	13.673%	$89.1537	$89.15	$89.15	$89.20
Purchase #2	$47.91	8.756%	$52.105	$52.11	$52.10	$52.10
Purchase #3	$43.80	12.464%	$49.2592	$49.26	$49.25	$49.30
Purchase #4	$176.53	3.174%	$182.1331	$182.13	$182.15	$182.10
Purchase #5	$49.72	5.380%	$52.3949	$52.39	$52.40	$52.40
Purchase #6	$28.80	13.307%	$32.6324	$32.63	$32.65	$32.60
Purchase #7	$127.85	8.641%	$138.8975	$138.90	$138.90	$138.90
7 purchase totals =	$553.04		$596.5758	$596.57	$596.60	$596.60