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	$89.99	11.665%	$100.4873	$100.49	$100.50	$100.50
Purchase #2	$78.81	5.597%	$83.221	$83.22	$83.20	$83.20
Purchase #3	$154.45	13.582%	$175.4274	$175.43	$175.45	$175.40
Purchase #4	$47.89	11.735%	$53.5099	$53.51	$53.50	$53.50
Purchase #5	$14.90	3.323%	$15.3951	$15.40	$15.40	$15.40
Purchase #6	$242.37	6.550%	$258.2452	$258.25	$258.25	$258.20
Purchase #7	$62.27	9.832%	$68.3924	$68.39	$68.40	$68.40
7 purchase totals =	$690.68		$754.6783	$754.69	$754.70	$754.60