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	$18.86	5.735%	$19.9416	$19.94	$19.95	$19.90
Purchase #2	$66.85	8.277%	$72.3832	$72.38	$72.40	$72.40
Purchase #3	$177.31	3.291%	$183.1453	$183.15	$183.15	$183.10
Purchase #4	$8.81	10.753%	$9.7573	$9.76	$9.75	$9.80
Purchase #5	$34.35	6.326%	$36.523	$36.52	$36.50	$36.50
Purchase #6	$78.56	4.867%	$82.3835	$82.38	$82.40	$82.40
Purchase #7	$90.85	10.297%	$100.2048	$100.20	$100.20	$100.20
7 purchase totals =	$475.59		$504.3387	$504.33	$504.35	$504.30