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	$155.48	11.608%	$173.5281	$173.53	$173.55	$173.50
Purchase #2	$84.78	6.723%	$90.4798	$90.48	$90.50	$90.50
Purchase #3	$42.56	13.518%	$48.3133	$48.31	$48.30	$48.30
Purchase #4	$213.44	11.710%	$238.4338	$238.43	$238.45	$238.40
Purchase #5	$155.49	8.199%	$168.2386	$168.24	$168.25	$168.20
Purchase #6	$7.41	13.175%	$8.3863	$8.39	$8.40	$8.40
Purchase #7	$209.60	10.639%	$231.8993	$231.90	$231.90	$231.90
7 purchase totals =	$868.76		$959.2792	$959.28	$959.35	$959.20