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	$99.78	4.577%	$104.3469	$104.35	$104.35	$104.30
Purchase #2	$221.58	13.226%	$250.8862	$250.89	$250.90	$250.90
Purchase #3	$201.64	8.535%	$218.85	$218.85	$218.85	$218.90
Purchase #4	$158.89	11.128%	$176.5713	$176.57	$176.55	$176.60
Purchase #5	$186.39	10.214%	$205.4279	$205.43	$205.45	$205.40
Purchase #6	$87.38	11.236%	$97.198	$97.20	$97.20	$97.20
Purchase #7	$13.85	10.535%	$15.3091	$15.31	$15.30	$15.30
7 purchase totals =	$969.51		$1,068.5894	$1,068.60	$1,068.60	$1,068.60