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	$234.43	9.591%	$256.9142	$256.91	$256.90	$256.90
Purchase #2	$50.67	5.200%	$53.3048	$53.30	$53.30	$53.30
Purchase #3	$43.90	8.143%	$47.4748	$47.47	$47.45	$47.50
Purchase #4	$64.96	4.803%	$68.08	$68.08	$68.10	$68.10
Purchase #5	$207.86	12.720%	$234.2998	$234.30	$234.30	$234.30
Purchase #6	$242.79	3.763%	$251.9262	$251.93	$251.95	$251.90
Purchase #7	$96.77	3.839%	$100.485	$100.49	$100.50	$100.50
7 purchase totals =	$941.38		$1,012.4848	$1,012.48	$1,012.50	$1,012.50