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	$36.49	9.829%	$40.0766	$40.08	$40.10	$40.10
Purchase #2	$181.60	3.257%	$187.5147	$187.51	$187.50	$187.50
Purchase #3	$197.40	9.142%	$215.4463	$215.45	$215.45	$215.40
Purchase #4	$184.95	3.168%	$190.8092	$190.81	$190.80	$190.80
Purchase #5	$78.42	10.780%	$86.8737	$86.87	$86.85	$86.90
Purchase #6	$249.34	13.440%	$282.8513	$282.85	$282.85	$282.90
Purchase #7	$130.87	10.402%	$144.4831	$144.48	$144.50	$144.50
7 purchase totals =	$1,059.07		$1,148.0549	$1,148.05	$1,148.05	$1,148.10