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	$205.67	12.462%	$231.3006	$231.30	$231.30	$231.30
Purchase #2	$225.72	12.792%	$254.5941	$254.59	$254.60	$254.60
Purchase #3	$112.86	13.526%	$128.1254	$128.13	$128.15	$128.10
Purchase #4	$83.49	11.133%	$92.7849	$92.78	$92.80	$92.80
Purchase #5	$46.30	5.687%	$48.9331	$48.93	$48.95	$48.90
Purchase #6	$144.32	5.256%	$151.9055	$151.91	$151.90	$151.90
Purchase #7	$180.51	11.166%	$200.6657	$200.67	$200.65	$200.70
7 purchase totals =	$998.87		$1,108.3093	$1,108.31	$1,108.35	$1,108.30