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	$235.84	9.440%	$258.1033	$258.10	$258.10	$258.10
Purchase #2	$37.34	13.742%	$42.4713	$42.47	$42.45	$42.50
Purchase #3	$210.75	8.718%	$229.1232	$229.12	$229.10	$229.10
Purchase #4	$39.32	3.257%	$40.6007	$40.60	$40.60	$40.60
Purchase #5	$233.95	9.481%	$256.1308	$256.13	$256.15	$256.10
Purchase #6	$14.76	11.455%	$16.4508	$16.45	$16.45	$16.50
Purchase #7	$94.62	4.159%	$98.5552	$98.56	$98.55	$98.60
7 purchase totals =	$866.58		$941.4353	$941.43	$941.40	$941.50