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	$167.61	12.453%	$188.4825	$188.48	$188.50	$188.50
Purchase #2	$83.48	8.262%	$90.3771	$90.38	$90.40	$90.40
Purchase #3	$237.59	5.869%	$251.5342	$251.53	$251.55	$251.50
Purchase #4	$233.64	8.314%	$253.0648	$253.06	$253.05	$253.10
Purchase #5	$76.28	13.458%	$86.5458	$86.55	$86.55	$86.50
Purchase #6	$162.81	10.230%	$179.4655	$179.47	$179.45	$179.50
Purchase #7	$138.43	8.137%	$149.694	$149.69	$149.70	$149.70
7 purchase totals =	$1,099.84		$1,199.1639	$1,199.16	$1,199.20	$1,199.20