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	$165.74	3.438%	$171.4381	$171.44	$171.45	$171.40
Purchase #2	$41.25	11.303%	$45.9125	$45.91	$45.90	$45.90
Purchase #3	$133.91	4.487%	$139.9185	$139.92	$139.90	$139.90
Purchase #4	$58.65	4.839%	$61.4881	$61.49	$61.50	$61.50
Purchase #5	$59.51	6.335%	$63.28	$63.28	$63.30	$63.30
Purchase #6	$165.94	7.389%	$178.2013	$178.20	$178.20	$178.20
Purchase #7	$71.34	10.509%	$78.8371	$78.84	$78.85	$78.80
7 purchase totals =	$696.34		$739.0756	$739.08	$739.10	$739.00