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	$25.64	12.839%	$28.9319	$28.93	$28.95	$28.90
Purchase #2	$249.68	8.727%	$271.4696	$271.47	$271.45	$271.50
Purchase #3	$40.89	13.745%	$46.5103	$46.51	$46.50	$46.50
Purchase #4	$187.35	9.640%	$205.4105	$205.41	$205.40	$205.40
Purchase #5	$124.51	12.843%	$140.5008	$140.50	$140.50	$140.50
Purchase #6	$18.80	8.627%	$20.4219	$20.42	$20.40	$20.40
Purchase #7	$36.76	12.597%	$41.3907	$41.39	$41.40	$41.40
7 purchase totals =	$683.63		$754.6357	$754.63	$754.60	$754.60