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	$14.34	8.845%	$15.6084	$15.61	$15.60	$15.60
Purchase #2	$171.60	13.180%	$194.2169	$194.22	$194.20	$194.20
Purchase #3	$113.91	6.556%	$121.3779	$121.38	$121.40	$121.40
Purchase #4	$139.72	8.815%	$152.0363	$152.04	$152.05	$152.00
Purchase #5	$182.76	12.414%	$205.4478	$205.45	$205.45	$205.40
Purchase #6	$162.33	13.559%	$184.3403	$184.34	$184.35	$184.30
Purchase #7	$139.52	3.168%	$143.94	$143.94	$143.95	$143.90
7 purchase totals =	$924.18		$1,016.9676	$1,016.98	$1,017.00	$1,016.80