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	$166.96	6.701%	$178.148	$178.15	$178.15	$178.10
Purchase #2	$150.60	3.571%	$155.9779	$155.98	$156.00	$156.00
Purchase #3	$103.53	12.142%	$116.1006	$116.10	$116.10	$116.10
Purchase #4	$69.61	5.227%	$73.2485	$73.25	$73.25	$73.20
Purchase #5	$194.71	11.152%	$216.4241	$216.42	$216.40	$216.40
Purchase #6	$91.83	13.606%	$104.3244	$104.32	$104.30	$104.30
Purchase #7	$137.32	12.439%	$154.4012	$154.40	$154.40	$154.40
7 purchase totals =	$914.56		$998.6247	$998.62	$998.60	$998.50