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	$129.53	11.716%	$144.7057	$144.71	$144.70	$144.70
Purchase #2	$17.60	5.472%	$18.5631	$18.56	$18.55	$18.60
Purchase #3	$93.48	7.571%	$100.5574	$100.56	$100.55	$100.60
Purchase #4	$31.70	4.348%	$33.0783	$33.08	$33.10	$33.10
Purchase #5	$41.85	13.253%	$47.3964	$47.40	$47.40	$47.40
Purchase #6	$150.84	9.189%	$164.7007	$164.70	$164.70	$164.70
Purchase #7	$89.78	5.575%	$94.7852	$94.79	$94.80	$94.80
7 purchase totals =	$554.78		$603.7868	$603.80	$603.80	$603.90