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	$23.38	6.231%	$24.8368	$24.84	$24.85	$24.80
Purchase #2	$125.98	10.203%	$138.8337	$138.83	$138.85	$138.80
Purchase #3	$185.42	8.336%	$200.8766	$200.88	$200.90	$200.90
Purchase #4	$73.51	13.270%	$83.2648	$83.26	$83.25	$83.30
Purchase #5	$159.55	12.348%	$179.2512	$179.25	$179.25	$179.30
Purchase #6	$71.60	10.169%	$78.881	$78.88	$78.90	$78.90
Purchase #7	$242.87	7.573%	$261.2625	$261.26	$261.25	$261.30
7 purchase totals =	$882.31		$967.2066	$967.20	$967.25	$967.30