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	$87.42	3.362%	$90.3591	$90.36	$90.35	$90.40
Purchase #2	$198.91	10.711%	$220.2153	$220.22	$220.20	$220.20
Purchase #3	$191.50	10.828%	$212.2356	$212.24	$212.25	$212.20
Purchase #4	$132.53	13.809%	$150.8311	$150.83	$150.85	$150.80
Purchase #5	$164.55	13.686%	$187.0703	$187.07	$187.05	$187.10
Purchase #6	$183.97	4.525%	$192.2946	$192.29	$192.30	$192.30
Purchase #7	$48.88	11.540%	$54.5208	$54.52	$54.50	$54.50
7 purchase totals =	$1,007.76		$1,107.5268	$1,107.53	$1,107.50	$1,107.50