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	$126.45	9.189%	$138.0695	$138.07	$138.05	$138.10
Purchase #2	$114.41	12.382%	$128.5762	$128.58	$128.60	$128.60
Purchase #3	$191.32	12.609%	$215.4435	$215.44	$215.45	$215.40
Purchase #4	$79.42	3.707%	$82.3641	$82.36	$82.35	$82.40
Purchase #5	$184.91	6.421%	$196.7831	$196.78	$196.80	$196.80
Purchase #6	$249.48	11.366%	$277.8359	$277.84	$277.85	$277.80
Purchase #7	$135.69	12.661%	$152.8697	$152.87	$152.85	$152.90
7 purchase totals =	$1,081.68		$1,191.9420	$1,191.94	$1,191.95	$1,192.00