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	$131.69	6.181%	$139.8298	$139.83	$139.85	$139.80
Purchase #2	$50.92	3.539%	$52.7221	$52.72	$52.70	$52.70
Purchase #3	$226.71	13.691%	$257.7489	$257.75	$257.75	$257.70
Purchase #4	$59.59	6.602%	$63.5241	$63.52	$63.50	$63.50
Purchase #5	$95.54	7.461%	$102.6682	$102.67	$102.65	$102.70
Purchase #6	$229.29	5.665%	$242.2793	$242.28	$242.30	$242.30
Purchase #7	$210.92	5.850%	$223.2588	$223.26	$223.25	$223.30
7 purchase totals =	$1,004.66		$1,082.0312	$1,082.03	$1,082.00	$1,082.00