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	$228.45	9.201%	$249.4697	$249.47	$249.45	$249.50
Purchase #2	$241.78	6.235%	$256.855	$256.86	$256.85	$256.90
Purchase #3	$14.55	13.208%	$16.4718	$16.47	$16.45	$16.50
Purchase #4	$86.36	7.602%	$92.9251	$92.93	$92.95	$92.90
Purchase #5	$89.68	11.343%	$99.8524	$99.85	$99.85	$99.90
Purchase #6	$83.43	8.588%	$90.595	$90.60	$90.60	$90.60
Purchase #7	$19.89	8.662%	$21.6129	$21.61	$21.60	$21.60
7 purchase totals =	$764.14		$827.7819	$827.79	$827.75	$827.90