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	$139.98	13.463%	$158.8255	$158.83	$158.85	$158.80
Purchase #2	$89.32	6.293%	$94.9409	$94.94	$94.95	$94.90
Purchase #3	$194.56	11.717%	$217.3566	$217.36	$217.35	$217.40
Purchase #4	$96.83	6.503%	$103.1269	$103.13	$103.15	$103.10
Purchase #5	$212.98	10.342%	$235.0064	$235.01	$235.00	$235.00
Purchase #6	$81.81	9.586%	$89.6523	$89.65	$89.65	$89.70
Purchase #7	$76.62	11.728%	$85.606	$85.61	$85.60	$85.60
7 purchase totals =	$892.10		$984.5146	$984.53	$984.55	$984.50