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	$43.98	11.664%	$49.1098	$49.11	$49.10	$49.10
Purchase #2	$51.69	8.472%	$56.0692	$56.07	$56.05	$56.10
Purchase #3	$200.78	11.681%	$224.2331	$224.23	$224.25	$224.20
Purchase #4	$133.68	3.432%	$138.2679	$138.27	$138.25	$138.30
Purchase #5	$184.31	6.676%	$196.6145	$196.61	$196.60	$196.60
Purchase #6	$45.55	4.116%	$47.4248	$47.42	$47.40	$47.40
Purchase #7	$201.32	13.520%	$228.5385	$228.54	$228.55	$228.50
7 purchase totals =	$861.31		$940.2578	$940.25	$940.20	$940.20