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	$241.59	3.620%	$250.3356	$250.34	$250.35	$250.30
Purchase #2	$171.35	9.617%	$187.8287	$187.83	$187.85	$187.80
Purchase #3	$62.71	6.555%	$66.8206	$66.82	$66.80	$66.80
Purchase #4	$74.39	9.520%	$81.4719	$81.47	$81.45	$81.50
Purchase #5	$114.53	3.246%	$118.2476	$118.25	$118.25	$118.20
Purchase #6	$54.30	10.351%	$59.9206	$59.92	$59.90	$59.90
Purchase #7	$110.54	13.646%	$125.6243	$125.62	$125.60	$125.60
7 purchase totals =	$829.41		$890.2493	$890.25	$890.20	$890.10