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	$183.66	6.478%	$195.5575	$195.56	$195.55	$195.60
Purchase #2	$146.77	5.421%	$154.7264	$154.73	$154.75	$154.70
Purchase #3	$143.29	9.438%	$156.8137	$156.81	$156.80	$156.80
Purchase #4	$150.85	11.393%	$168.0363	$168.04	$168.05	$168.00
Purchase #5	$104.46	10.629%	$115.5631	$115.56	$115.55	$115.60
Purchase #6	$72.83	11.301%	$81.0605	$81.06	$81.05	$81.10
Purchase #7	$107.30	4.157%	$111.7605	$111.76	$111.75	$111.80
7 purchase totals =	$909.16		$983.5180	$983.52	$983.50	$983.60