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	$235.57	8.392%	$255.339	$255.34	$255.35	$255.30
Purchase #2	$177.83	6.805%	$189.9313	$189.93	$189.95	$189.90
Purchase #3	$135.86	7.347%	$145.8416	$145.84	$145.85	$145.80
Purchase #4	$145.98	5.467%	$153.9607	$153.96	$153.95	$154.00
Purchase #5	$200.77	11.248%	$223.3526	$223.35	$223.35	$223.40
Purchase #6	$38.52	10.599%	$42.6027	$42.60	$42.60	$42.60
Purchase #7	$131.83	12.619%	$148.4656	$148.47	$148.45	$148.50
7 purchase totals =	$1,066.36		$1,159.4935	$1,159.49	$1,159.50	$1,159.50