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	$22.43	6.532%	$23.8951	$23.90	$23.90	$23.90
Purchase #2	$29.54	5.605%	$31.1957	$31.20	$31.20	$31.20
Purchase #3	$119.50	9.873%	$131.2982	$131.30	$131.30	$131.30
Purchase #4	$74.98	13.189%	$84.8691	$84.87	$84.85	$84.90
Purchase #5	$131.54	8.399%	$142.588	$142.59	$142.60	$142.60
Purchase #6	$49.97	9.836%	$54.885	$54.89	$54.90	$54.90
Purchase #7	$54.57	7.808%	$58.8308	$58.83	$58.85	$58.80
7 purchase totals =	$482.53		$527.5619	$527.58	$527.60	$527.60