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	$18.48	4.711%	$19.3506	$19.35	$19.35	$19.40
Purchase #2	$237.60	11.870%	$265.8031	$265.80	$265.80	$265.80
Purchase #3	$170.79	7.154%	$183.0083	$183.01	$183.00	$183.00
Purchase #4	$107.91	3.328%	$111.5012	$111.50	$111.50	$111.50
Purchase #5	$98.53	10.323%	$108.7013	$108.70	$108.70	$108.70
Purchase #6	$131.35	10.800%	$145.5358	$145.54	$145.55	$145.50
Purchase #7	$217.45	13.750%	$247.3494	$247.35	$247.35	$247.30
7 purchase totals =	$982.11		$1,081.2497	$1,081.25	$1,081.25	$1,081.20