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	$226.78	11.791%	$253.5196	$253.52	$253.50	$253.50
Purchase #2	$15.89	7.789%	$17.1277	$17.13	$17.15	$17.10
Purchase #3	$119.41	3.703%	$123.8318	$123.83	$123.85	$123.80
Purchase #4	$24.99	11.553%	$27.8771	$27.88	$27.90	$27.90
Purchase #5	$241.66	10.677%	$267.462	$267.46	$267.45	$267.50
Purchase #6	$230.46	11.494%	$256.9491	$256.95	$256.95	$256.90
Purchase #7	$31.91	4.298%	$33.2815	$33.28	$33.30	$33.30
7 purchase totals =	$891.10		$980.0488	$980.05	$980.10	$980.00