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	$14.94	10.368%	$16.489	$16.49	$16.50	$16.50
Purchase #2	$72.25	13.820%	$82.235	$82.24	$82.25	$82.20
Purchase #3	$102.55	4.194%	$106.8509	$106.85	$106.85	$106.90
Purchase #4	$142.69	5.777%	$150.9332	$150.93	$150.95	$150.90
Purchase #5	$124.80	11.208%	$138.7876	$138.79	$138.80	$138.80
Purchase #6	$51.58	3.863%	$53.5725	$53.57	$53.55	$53.60
Purchase #7	$106.67	4.835%	$111.8275	$111.83	$111.85	$111.80
7 purchase totals =	$615.48		$660.6957	$660.70	$660.75	$660.70