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	$142.81	12.421%	$160.5484	$160.55	$160.55	$160.50
Purchase #2	$181.74	9.787%	$199.5269	$199.53	$199.55	$199.50
Purchase #3	$19.64	6.252%	$20.8679	$20.87	$20.85	$20.90
Purchase #4	$142.86	12.606%	$160.8689	$160.87	$160.85	$160.90
Purchase #5	$232.93	12.161%	$261.2566	$261.26	$261.25	$261.30
Purchase #6	$138.92	5.713%	$146.8565	$146.86	$146.85	$146.90
Purchase #7	$92.83	8.178%	$100.4216	$100.42	$100.40	$100.40
7 purchase totals =	$951.73		$1,050.3468	$1,050.36	$1,050.30	$1,050.40