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	$24.29	6.186%	$25.7926	$25.79	$25.80	$25.80
Purchase #2	$101.40	7.374%	$108.8772	$108.88	$108.90	$108.90
Purchase #3	$14.46	10.124%	$15.9239	$15.92	$15.90	$15.90
Purchase #4	$212.46	13.621%	$241.3992	$241.40	$241.40	$241.40
Purchase #5	$42.84	5.753%	$45.3046	$45.30	$45.30	$45.30
Purchase #6	$127.78	8.787%	$139.008	$139.01	$139.00	$139.00
Purchase #7	$14.42	5.536%	$15.2183	$15.22	$15.20	$15.20
7 purchase totals =	$537.65		$591.5238	$591.52	$591.50	$591.50