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	$138.54	11.342%	$154.2532	$154.25	$154.25	$154.30
Purchase #2	$219.80	7.295%	$235.8344	$235.83	$235.85	$235.80
Purchase #3	$143.87	12.641%	$162.0566	$162.06	$162.05	$162.10
Purchase #4	$61.65	11.271%	$68.5986	$68.60	$68.60	$68.60
Purchase #5	$6.72	5.123%	$7.0643	$7.06	$7.05	$7.10
Purchase #6	$183.34	9.272%	$200.3393	$200.34	$200.35	$200.30
Purchase #7	$156.27	11.370%	$174.0379	$174.04	$174.05	$174.00
7 purchase totals =	$910.19		$1,002.1843	$1,002.18	$1,002.20	$1,002.20