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	$30.77	7.757%	$33.1568	$33.16	$33.15	$33.20
Purchase #2	$59.90	3.617%	$62.0666	$62.07	$62.05	$62.10
Purchase #3	$205.84	13.548%	$233.7272	$233.73	$233.75	$233.70
Purchase #4	$41.48	13.772%	$47.1926	$47.19	$47.20	$47.20
Purchase #5	$146.92	5.847%	$155.5104	$155.51	$155.50	$155.50
Purchase #6	$43.78	10.804%	$48.51	$48.51	$48.50	$48.50
Purchase #7	$163.98	12.464%	$184.4185	$184.42	$184.40	$184.40
7 purchase totals =	$692.67		$764.5821	$764.59	$764.55	$764.60