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	$22.47	7.599%	$24.1775	$24.18	$24.20	$24.20
Purchase #2	$133.85	5.810%	$141.6267	$141.63	$141.65	$141.60
Purchase #3	$97.34	8.749%	$105.8563	$105.86	$105.85	$105.90
Purchase #4	$11.63	6.792%	$12.4199	$12.42	$12.40	$12.40
Purchase #5	$180.54	8.822%	$196.4672	$196.47	$196.45	$196.50
Purchase #6	$92.84	5.150%	$97.6213	$97.62	$97.60	$97.60
Purchase #7	$119.33	10.140%	$131.4301	$131.43	$131.45	$131.40
7 purchase totals =	$658.00		$709.5990	$709.61	$709.60	$709.60