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	$131.82	8.850%	$143.4861	$143.49	$143.50	$143.50
Purchase #2	$103.32	7.801%	$111.38	$111.38	$111.40	$111.40
Purchase #3	$11.38	10.242%	$12.5455	$12.55	$12.55	$12.50
Purchase #4	$179.30	6.800%	$191.4924	$191.49	$191.50	$191.50
Purchase #5	$130.63	5.571%	$137.9074	$137.91	$137.90	$137.90
Purchase #6	$51.34	10.426%	$56.6927	$56.69	$56.70	$56.70
Purchase #7	$25.47	12.233%	$28.5857	$28.59	$28.60	$28.60
7 purchase totals =	$633.26		$682.0898	$682.10	$682.15	$682.10