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	$15.34	7.659%	$16.5149	$16.51	$16.50	$16.50
Purchase #2	$97.65	8.196%	$105.6534	$105.65	$105.65	$105.70
Purchase #3	$164.50	11.684%	$183.7202	$183.72	$183.70	$183.70
Purchase #4	$164.35	5.345%	$173.1345	$173.13	$173.15	$173.10
Purchase #5	$245.29	5.552%	$258.9085	$258.91	$258.90	$258.90
Purchase #6	$40.31	7.666%	$43.4002	$43.40	$43.40	$43.40
Purchase #7	$191.38	10.174%	$210.851	$210.85	$210.85	$210.90
7 purchase totals =	$918.82		$992.1827	$992.17	$992.15	$992.20