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	$155.39	5.845%	$164.4725	$164.47	$164.45	$164.50
Purchase #2	$50.77	13.682%	$57.7164	$57.72	$57.70	$57.70
Purchase #3	$145.92	7.263%	$156.5182	$156.52	$156.50	$156.50
Purchase #4	$91.30	3.540%	$94.532	$94.53	$94.55	$94.50
Purchase #5	$140.93	11.146%	$156.6381	$156.64	$156.65	$156.60
Purchase #6	$178.76	6.244%	$189.9218	$189.92	$189.90	$189.90
Purchase #7	$59.43	11.418%	$66.2157	$66.22	$66.20	$66.20
7 purchase totals =	$822.50		$886.0147	$886.02	$885.95	$885.90