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	$227.93	11.627%	$254.4314	$254.43	$254.45	$254.40
Purchase #2	$98.60	5.364%	$103.8889	$103.89	$103.90	$103.90
Purchase #3	$154.57	9.400%	$169.0996	$169.10	$169.10	$169.10
Purchase #4	$220.26	4.137%	$229.3722	$229.37	$229.35	$229.40
Purchase #5	$111.61	7.360%	$119.8245	$119.82	$119.80	$119.80
Purchase #6	$243.49	13.211%	$275.6575	$275.66	$275.65	$275.70
Purchase #7	$240.93	5.352%	$253.8246	$253.82	$253.80	$253.80
7 purchase totals =	$1,297.39		$1,406.0987	$1,406.09	$1,406.05	$1,406.10