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	$124.31	12.123%	$139.3801	$139.38	$139.40	$139.40
Purchase #2	$78.47	13.740%	$89.2518	$89.25	$89.25	$89.30
Purchase #3	$185.70	10.740%	$205.6442	$205.64	$205.65	$205.60
Purchase #4	$77.55	13.427%	$87.9626	$87.96	$87.95	$88.00
Purchase #5	$214.57	13.742%	$244.0562	$244.06	$244.05	$244.10
Purchase #6	$97.32	8.714%	$105.8005	$105.80	$105.80	$105.80
Purchase #7	$154.29	3.491%	$159.6763	$159.68	$159.70	$159.70
7 purchase totals =	$932.21		$1,031.7717	$1,031.77	$1,031.80	$1,031.90