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	$85.50	4.746%	$89.5578	$89.56	$89.55	$89.60
Purchase #2	$160.53	8.429%	$174.0611	$174.06	$174.05	$174.10
Purchase #3	$95.79	9.570%	$104.9571	$104.96	$104.95	$105.00
Purchase #4	$100.52	4.463%	$105.0062	$105.01	$105.00	$105.00
Purchase #5	$235.78	9.554%	$258.3064	$258.31	$258.30	$258.30
Purchase #6	$130.30	4.518%	$136.187	$136.19	$136.20	$136.20
Purchase #7	$53.75	13.230%	$60.8611	$60.86	$60.85	$60.90
7 purchase totals =	$862.17		$928.9367	$928.95	$928.90	$929.10