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	$34.72	13.633%	$39.4534	$39.45	$39.45	$39.50
Purchase #2	$126.37	8.299%	$136.8574	$136.86	$136.85	$136.90
Purchase #3	$202.82	8.218%	$219.4877	$219.49	$219.50	$219.50
Purchase #4	$46.80	7.498%	$50.3091	$50.31	$50.30	$50.30
Purchase #5	$132.52	7.738%	$142.7744	$142.77	$142.75	$142.80
Purchase #6	$184.87	11.149%	$205.4812	$205.48	$205.50	$205.50
Purchase #7	$104.79	4.834%	$109.8555	$109.86	$109.85	$109.90
7 purchase totals =	$832.89		$904.2187	$904.22	$904.20	$904.40