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	$232.89	10.301%	$256.88	$256.88	$256.90	$256.90
Purchase #2	$89.50	13.808%	$101.8582	$101.86	$101.85	$101.90
Purchase #3	$38.60	5.299%	$40.6454	$40.65	$40.65	$40.60
Purchase #4	$37.31	5.228%	$39.2606	$39.26	$39.25	$39.30
Purchase #5	$123.63	10.456%	$136.5568	$136.56	$136.55	$136.60
Purchase #6	$45.52	9.592%	$49.8863	$49.89	$49.90	$49.90
Purchase #7	$132.64	9.225%	$144.876	$144.88	$144.90	$144.90
7 purchase totals =	$700.09		$769.9633	$769.98	$770.00	$770.10