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	$100.88	3.379%	$104.2887	$104.29	$104.30	$104.30
Purchase #2	$22.46	6.569%	$23.9354	$23.94	$23.95	$23.90
Purchase #3	$63.94	13.869%	$72.8078	$72.81	$72.80	$72.80
Purchase #4	$122.30	13.773%	$139.1444	$139.14	$139.15	$139.10
Purchase #5	$201.32	10.236%	$221.9271	$221.93	$221.95	$221.90
Purchase #6	$19.86	10.219%	$21.8895	$21.89	$21.90	$21.90
Purchase #7	$58.50	10.615%	$64.7098	$64.71	$64.70	$64.70
7 purchase totals =	$589.26		$648.7027	$648.71	$648.75	$648.60