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	$163.59	3.124%	$168.7006	$168.70	$168.70	$168.70
Purchase #2	$137.33	9.607%	$150.5233	$150.52	$150.50	$150.50
Purchase #3	$85.79	5.108%	$90.1722	$90.17	$90.15	$90.20
Purchase #4	$246.46	9.264%	$269.2921	$269.29	$269.30	$269.30
Purchase #5	$126.31	5.379%	$133.1042	$133.10	$133.10	$133.10
Purchase #6	$153.38	12.325%	$172.2841	$172.28	$172.30	$172.30
Purchase #7	$13.88	10.593%	$15.3503	$15.35	$15.35	$15.40
7 purchase totals =	$926.74		$999.4268	$999.41	$999.40	$999.50