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	$183.78	12.555%	$206.8536	$206.85	$206.85	$206.90
Purchase #2	$39.49	9.531%	$43.2538	$43.25	$43.25	$43.30
Purchase #3	$169.69	7.333%	$182.1334	$182.13	$182.15	$182.10
Purchase #4	$82.40	9.763%	$90.4447	$90.44	$90.45	$90.40
Purchase #5	$170.79	6.207%	$181.3909	$181.39	$181.40	$181.40
Purchase #6	$125.67	13.605%	$142.7674	$142.77	$142.75	$142.80
Purchase #7	$12.31	5.870%	$13.0326	$13.03	$13.05	$13.00
7 purchase totals =	$784.13		$859.8764	$859.86	$859.90	$859.90