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	$8.87	10.685%	$9.8178	$9.82	$9.80	$9.80
Purchase #2	$212.88	4.443%	$222.3383	$222.34	$222.35	$222.30
Purchase #3	$169.82	3.863%	$176.3801	$176.38	$176.40	$176.40
Purchase #4	$10.90	5.557%	$11.5057	$11.51	$11.50	$11.50
Purchase #5	$232.59	11.719%	$259.8472	$259.85	$259.85	$259.80
Purchase #6	$82.44	9.293%	$90.1011	$90.10	$90.10	$90.10
Purchase #7	$136.82	10.542%	$151.2436	$151.24	$151.25	$151.20
7 purchase totals =	$854.32		$921.2338	$921.24	$921.25	$921.10