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	$89.78	10.694%	$99.3811	$99.38	$99.40	$99.40
Purchase #2	$172.80	5.456%	$182.228	$182.23	$182.25	$182.20
Purchase #3	$31.30	6.160%	$33.2281	$33.23	$33.25	$33.20
Purchase #4	$141.97	12.540%	$159.773	$159.77	$159.75	$159.80
Purchase #5	$76.99	5.792%	$81.4493	$81.45	$81.45	$81.40
Purchase #6	$191.85	11.843%	$214.5708	$214.57	$214.55	$214.60
Purchase #7	$238.86	11.194%	$265.598	$265.60	$265.60	$265.60
7 purchase totals =	$943.55		$1,036.2283	$1,036.23	$1,036.25	$1,036.20