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	$243.72	9.382%	$266.5858	$266.59	$266.60	$266.60
Purchase #2	$162.73	11.754%	$181.8573	$181.86	$181.85	$181.90
Purchase #3	$218.76	10.147%	$240.9576	$240.96	$240.95	$241.00
Purchase #4	$31.69	7.782%	$34.1561	$34.16	$34.15	$34.20
Purchase #5	$82.86	3.185%	$85.4991	$85.50	$85.50	$85.50
Purchase #6	$42.31	10.125%	$46.5939	$46.59	$46.60	$46.60
Purchase #7	$132.26	9.498%	$144.8221	$144.82	$144.80	$144.80
7 purchase totals =	$914.33		$1,000.4719	$1,000.48	$1,000.45	$1,000.60