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	$72.96	12.185%	$81.8502	$81.85	$81.85	$81.90
Purchase #2	$225.49	13.661%	$256.2942	$256.29	$256.30	$256.30
Purchase #3	$163.52	6.315%	$173.8463	$173.85	$173.85	$173.80
Purchase #4	$155.52	13.828%	$177.0253	$177.03	$177.05	$177.00
Purchase #5	$124.91	8.337%	$135.3237	$135.32	$135.30	$135.30
Purchase #6	$58.84	11.523%	$65.6201	$65.62	$65.60	$65.60
Purchase #7	$171.66	10.874%	$190.3263	$190.33	$190.35	$190.30
7 purchase totals =	$972.90		$1,080.2861	$1,080.29	$1,080.30	$1,080.20