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	$221.94	9.198%	$242.354	$242.35	$242.35	$242.40
Purchase #2	$46.32	10.386%	$51.1308	$51.13	$51.15	$51.10
Purchase #3	$133.50	6.335%	$141.9572	$141.96	$141.95	$142.00
Purchase #4	$112.94	5.472%	$119.1201	$119.12	$119.10	$119.10
Purchase #5	$149.85	12.713%	$168.9004	$168.90	$168.90	$168.90
Purchase #6	$152.61	10.382%	$168.454	$168.45	$168.45	$168.50
Purchase #7	$38.33	5.691%	$40.5114	$40.51	$40.50	$40.50
7 purchase totals =	$855.49		$932.4279	$932.42	$932.40	$932.50