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	$230.94	12.758%	$260.4033	$260.40	$260.40	$260.40
Purchase #2	$120.72	11.467%	$134.563	$134.56	$134.55	$134.60
Purchase #3	$120.99	9.496%	$132.4792	$132.48	$132.50	$132.50
Purchase #4	$97.96	10.729%	$108.4701	$108.47	$108.45	$108.50
Purchase #5	$230.69	11.392%	$256.9702	$256.97	$256.95	$257.00
Purchase #6	$68.90	4.765%	$72.1831	$72.18	$72.20	$72.20
Purchase #7	$72.34	8.335%	$78.3695	$78.37	$78.35	$78.40
7 purchase totals =	$942.54		$1,043.4384	$1,043.43	$1,043.40	$1,043.60